Can I Specify Title Page Customization in a Template Instead of My Document?

Question

I'm trying to create a LaTeX beamer theme to match the official PowerPoint template of Rutgers University. I've been able to create the title page, and this MWE

\documentclass{beamer}
    \usepackage{graphicx}
    \usetheme{NewBrunswick}

    \title{This Is A Long Descriptive Title Describing How Much Easier It Would Be To 
        Study \LaTeX{} And Not Hypersonics}
    \author{Someone Other Than Till Tantau}
    \institute[MAE]{Fake Degree Candidate \and Mechanical \& Aerospace Engineering}
    \date{A Long, Long, Time Ago}

\begin{document}
{
\usebackgroundtemplate{
    \includegraphics[width=\paperwidth, height=\paperheight]{rutgersTitle} }
    \begin{frame}[plain]
        \titlepage
    \end{frame} }
\end{document}

with this MWE beamerthemeNewBrunswick.sty file

\setbeamercolor{titlelike}{fg=white}
\setbeamercolor{title page}{fg=white}
\setbeamertemplate{navigation symbols}{}
\setbeamerfont{title page}{family=\rmfamily}
\addtobeamertemplate{title page}{\vspace{3\baselineskip}}{}

resembles it:

Is there a way for me to take the background image code out of the document, and into a/the theme file? I would like to distribute this so users can just specify

\begin{frame}[plain]
    \titlepage
\end{frame}

and get the background image that I've stored with the theme files. I tried adding this to the theme file

\addtobeamertemplate{title page}{}{
    \usebackgroundtemplate{
        \includegraphics[width=\paperwidth, height=\paperheight]{rutgersTitle} } }

but it doesn't add the background image as I had hoped.

EDIT:

Trying textpos with

\documentclass{beamer}
    \usepackage{graphicx}
    \usetheme{NewBrunswick}

    \title{This Is A Long Descriptive Title Describing How Much Easier It Would Be To
        Study \LaTeX{} And Not Hypersonics}
    \author{Someone Other Than Till Tantau}
    \institute[MAE]{Fake Degree Candidate \and
                    Mechanical \& Aerospace Engineering}
    \date{A Long, Long, Time Ago}

\begin{document}
    \begin{frame}[plain]
        \titlepage
    \end{frame}
\end{document}

where beamerthemeNewBrunswick.sty now contains

\RequirePackage{textpos}

\setbeamercolor{titlelike}{fg=white}
\setbeamercolor{title page}{fg=white}
\setbeamertemplate{navigation symbols}{}
\setbeamerfont{title page}{family=\rmfamily}
\addtobeamertemplate{title page}{\vspace{3\baselineskip}}{}

\addtobeamertemplate{title page}{
    \begin{textblock*}{\paperwidth}(-2.6em, -1.6em)
        \includegraphics[width=\paperwidth, height=\paperheight]{rutgersTitle}
    \end{textblock*} }{}

produces where you can see there's an additional white bar on the bottom. Did I use textpos incorrectly? Here is my background image: I guess I should be adding to the question instead of comments. Is textpos using a centering-like effect here? If I add something like

\addtobeamertemplate{title page}{\vspace{10\baselineskip}}{}

the background image moves up the slide and my text moves down the slide.

EDIT WITH SOLUTION: Using Tikz appeared to be the only way to avoid hard coding sizes, so I went with it despite increased compile time. My final code for the .sty file was:

\RequirePackage{tikz}

\setbeamercolor{titlelike}{fg=white}
\setbeamercolor{title page}{fg=white}
\setbeamertemplate{navigation symbols}{}
\setbeamerfont{title page}{family=\rmfamily}
\addtobeamertemplate{title page}{\vspace{3\baselineskip}}{}

\addtobeamertemplate{title page}{
    \begin{tikzpicture}[remember picture,overlay]
        \node [xshift=0cm,yshift=0cm] at (current page.center) {
            \includegraphics[width=\paperwidth, height=\paperheight]{rutgersTitle}
        };
        \node [xshift=0cm,yshift=0cm] at (0.04\paperwidth,-0.01\paperheight) {
            \includegraphics[width=3cm]{tigre}
        };
    \end{tikzpicture}
}{}

Answer 1

Try with this beamerthemeNewBrunswick.sty file; the idea is to use the TikZ package to add the background image at an absolute position; of course, using several nodes you can add several images; for example, defining beamerthemeNewBrunswick.sty in the following way:

\RequirePackage{tikz}

\setbeamercolor{titlelike}{fg=white}
\setbeamercolor{title page}{fg=white}
\setbeamertemplate{navigation symbols}{}
\setbeamerfont{title page}{family=\rmfamily}
\addtobeamertemplate{title page}{\vspace{3\baselineskip}}{}

\addtobeamertemplate{title page}{%
\begin{tikzpicture}[remember picture,overlay] 
  \node [xshift=0cm,yshift=0cm] at (current page.center)
  {\includegraphics[width=\paperwidth, height=\paperheight]{rutgersTitle}};             
  \node [xshift=0cm,yshift=0cm] at (1cm,-0.7\paperheight)
  {\includegraphics[width=3cm]{tigre}};             
\end{tikzpicture}%
}{}


\RequirePackage{textpos}

\setbeamercolor{title}{fg=white}
\setbeamercolor{subtitle}{fg=white}
\setbeamercolor{author}{fg=white}
\setbeamercolor{institute}{fg=white}
\setbeamercolor{date}{fg=white}
\setbeamertemplate{navigation symbols}{}
\setbeamerfont{title page}{family=\rmfamily}

\addtobeamertemplate{title page}{%
\begin{textblock*}{\paperwidth}(-2.6em,-1.6em)
\includegraphics[width=\paperwidth, height=\paperheight]{tigre} 
\end{textblock*}%
\begin{textblock*}{2cm}(0cm,6cm)
\includegraphics[width=2cm]{tigre} 
\end{textblock*}
}{}

and using the following .tex file:

\documentclass{beamer}
\usepackage{graphicx}
\usetheme{NewBrunswick}

\title{This Is A Long Descriptive Title Describing How Much Easier It Would Be To
        Study \LaTeX{} And Not Hypersonics}
\author{Someone Other Than Till Tantau}
\institute[MAE]{Fake Degree Candidate \and
                    Mechanical \& Aerospace Engineering}
\date{A Long, Long, Time Ago}

\begin{document}

\begin{frame}
\titlepage
\end{frame}

\end{document}

you'll get