"Handout" on Title Slide – \addtobeamertemplate

I'd like to use \addtobeamertemplate{} to modify the title page to include a »Handout«, when slides are set in handout mode.

\mode<handout>{\addtobeamertemplate{title page}{}{\quad \emph{Handout Version}}}

But the call to \addtobeamertemplate{} seems to be without effect. Why?

MWE

\documentclass{beamer}
\usetheme{Juelich}

\title{Minimal Working Example}
\subtitle{To use addtobeamertemplate}
\author{Andreas Herten}
\date{\today}
\institute{JSC}

\addtobeamertemplate{title page}{}{\quad \emph{It works!}}

\begin{document}

\maketitle

\end{document}