beamer table of contents shade all previous sections

Question

How do I shade in a LaTeX beamer only the previous sections but not the following sections?

Just right now I have something like

\documentclass{beamer}

\begin{document}

\section{Section1}
\section{Section2}
\tableofcontents[currentsection] 
\section{Section3}
\frame{}

\end{document}

which leads to a TOC which highlights Section2 and shades the other sections . The desired behaviour would be to highlight Section2 and Section3 and shade only Section1

Answer 1

This answer gave me the clue (thanks to @AndrewUzzel). Splitting in two parts and using two tocs solved it, however spacing needs to be adjusted. Here is the miminal example:

\documentclass{beamer}

\begin{document}
\part{one}
\section{Section1}
\part{two}
\section{Section2}
\frame{
\tableofcontents[part=1,currentsection]\tableofcontents
}
\section{Section3}
\frame{}

\end{document}