Beamer: set mode mid-presentation

Question

In Beamer, is it possible to switch between handout mode and presentation mode in the middle of a presentation?

The reason I want to do this is that I am working through a slide deck in multiple lectures. I want to omit the pauses for slides from previous lectures to support quickly navigating to them for reference (handout mode), while for the current lecture I would like to include the pauses for presentation purposes (presentation mode).

Here's a minimal example:

\documentclass[pdftex,handout]{beamer}

\begin{document}

\begin{frame}{Frame 1}
Step 1 \pause Step 2 \pause Step 3
\end{frame}

% I want to switch to presentation mode here!

\begin{frame}{Frame 2}
Step 4 \pause Step 5 \pause Step 6
\end{frame}

\end{document}

After compiling, I would like to have four slides. One slide showing the entire Frame 1, and three slides showing the three stages of Frame 2.

Answer 1

beamer holds the selected mode in the macro \beamer@currentmode so what you need to do is change that mid-way through your document.

\documentclass[pdftex,handout]{beamer}
%\url{http://tex.stackexchange.com/q/91691/86}

\makeatletter
\newcommand\changemode[1]{%
  \gdef\beamer@currentmode{#1}}
\makeatother

\begin{document}

\begin{frame}{Frame 1}
Step 1 \pause Step 2 \pause Step 3
\end{frame}

% I want to switch to presentation mode here!
\changemode{beamer}

\begin{frame}{Frame 2}
Step 4 \pause Step 5 \pause Step 6
\end{frame}

\end{document}

Of course, there may be things "under the bonnet" which depend on the mode during initialisation so it might be that you want to start in beamer mode, switch to handout (or maybe trans) at the start of the slides, then back to beamer for the slides for the current lecture.