\documentclass{beamer}
\usepackage{filecontents,listings}
\usepackage{showexpl}
\makeatletter
  \let\deactivate=\SX@@preset
\makeatother
\begin{filecontents*}{foo.tex}
\documentclass{article}
\begin{document}
\huge\TeX\ and \LaTeX
\end{document}
\end{filecontents*}
\begin{document}
\begin{frame}

\begin{minipage}{.55\textwidth}
  \lstinputlisting{foo.tex}
\end{minipage}\pause
\hfill
\begin{minipage}{.4\textwidth}
  \deactivate
  \input{foo.tex}
\end{minipage}
\end{frame}

\end{document}
