adding co-authors to customised title page for beamer presentation

Question

I have customised my title page, using \title \date and \institute. I would like to add another line with co-authors, but I couldn't find any examples of how to do it. My ideas at the moment are

1. I could hi-jack \insertshortinstitute, since I don't use this in anywhere else.
2. I could define a new variable e.g. \def\mycoauthor{} (like on Use the values of \title, \author and \date on a custom title page) but then I don't know how to access it, especially since my maketitle definite is in a separate style file.

Here is a MWE showing how I create the title page at the moment, and an attempt to include coauthors:

\documentclass{beamer} 
\usetheme{_MWE}

\title[short title]{TITLE TITLE TITLE TITLE TITLE TITLE}
\author[me]{A. U. Thor}
\def\coauthors{A. N. Other, J. Bloggs, J. Doe}
\institute[\coauthors]{My Institute}
\date{1.1.2012}

\begin{document}
\maketitle
\end{document}

beamertheme_MWE.sty:

\ProvidesPackage{beamertheme_MWE}

\makeatletter
\def\maketitle{%
\begin{frame}[plain]
{%
 \vspace{10mm}
 \parbox{122mm}%
  {%
   \centering
   {\Large \inserttitle}\\
   \vspace{8mm}
   {\large \insertauthor}\\
   \vspace{3mm}
   {\large \insertshortinstitute}
   \vspace{7mm}
   {\small \insertinstitute}\\
   \vspace{-5mm}
   {\flushleft
    \hspace{1mm}
    LOGO1
    \hspace{60mm}
    \raisebox{0.5mm}{
        LOGO2
    \hspace{10mm}
    }
  }\\
  \vspace{0mm}
  {
   \parbox{53mm}{\centering \small \insertdate\\
   }
  }
 }
}
\end{frame}
  }
\makeatother

incidentally... why doesn't the \centering command work for \insertshortinstitute, and why do I get an error "there's no line here to end" if I put a \\ after it, as I do with \author etc.?

Answer 1

I think \author uses a minipage internally, so you can use something like

\author[me]{A. U. Thor\\[3mm]A. N. Other, J. Bloggs, J. Doe}

and forget \coauthors except you want to use them somewhere else.

If you use this construction, delete \insertshortinstitue form your style.