Bifurcating a PDF: choosing a "Plan B" during a talk

Question

I think this is a greenhorn's question, but anyway. It is sometimes difficult to measure time for a talk, according to unknown places and audiences.By this and other reasons I'd like to subtly launch a hidden "Plan B" (or, why not, a longer plan C) during my talk. Specifically

Question: Is it possible to generate a PDF that allows one to take decisions when giving a talk. That is, if at some point of the talk, one notices that one ran out of time, to manually choose a shorter sequence of slides?

(The optimal solution may be having enough practice giving talks - not my case)

Answer 1

Merging some of the suggestions, an answer boils down to the code below. Here, one has introduced a pair of links (with\hyperlink) in a strategic slide. When on that slide, one sees the remaining time and decides one of three options: go ahead with the normal presentation; take a shorter Plan B, which can be further reduced by skipping proofs; or take a longer path, Plan C by clicking the frame title.

\documentclass[english]{beamer}
\usepackage{babel}
\usetheme{Berlin}
\begin{document}

\begin{frame}
% this hyperlink leads to a longer PlanC,
% if there is enough time
\frametitle{\hyperlink{planC}{Strategic slide (planed)}}
\begin{itemize}
 \item 
Is your time, say, less 20 minutes?  $\Rightarrow$ click the TeX.SE logo:
 \item Have you abount 30 minutes $\Rightarrow$ click nothing and go ahead.
 \item You have much more than 30 min. $\Rightarrow$ click the frame title
\end{itemize}
\begin{flushright}
\vspace{-4cm}
% this hyperlink leads to a 
% shorter ``plan B''
\hyperlink{planB}{
\includegraphics[width=4cm]{tex.jpg}}
\end{flushright}
\end{frame}

\begin{frame}
\frametitle{Part of the usual course of the Talk}
\begin{flushright}
\vspace{-2cm}
\includegraphics[width=4cm]{tex.jpg}
\end{flushright}
Any thing here...
\end{frame}

\begin{frame}[label=planB]
\frametitle{Plan B}
\begin{flushright}
\vspace{-.2cm}
\includegraphics[width=4cm]{tex.jpg}
\end{flushright}
Set of Slides sumarizing what would have being a 
talk without hurries.\\

To sumarize even more, the proof
of the following theorem can be skipped.
\begin{beamerboxesrounded}[upper=uppercol,lower=lowercol,shadow=true]{Theorem}[Pythagoras]
\[a^2+b^2=c^2\]
\end{beamerboxesrounded}
% this link leads to the slide
% just after the proof.
\hyperlink{nexttoproof}{Skip proof.} 
\end{frame}

\begin{frame}[label=planB]
% one arrives to this slide
% slide by clicking the TeX.SE 
% logo in the first slide. 
\frametitle{Proof of the Theorem}
\begin{flushright}
\vspace{-2cm}
\includegraphics[width=4cm]{tex.jpg}
\end{flushright}
This slide was skipped by clicking 
``Skip proof'' in the previous one.
\end{frame}

\begin{frame}[label=nexttoproof]
\frametitle{After the proof}
\begin{flushright}
\vspace{-2cm}
\includegraphics[width=4cm]{tex.jpg}
\end{flushright}
Set of Slides sumarizing what would have being a 
talk without hurries.
\end{frame}

\begin{frame}[label=planC]
% one arrives to this 
% slide by clicking the frame
% in the first slide. 
\frametitle{Plan C}
\begin{flushright}
\vspace{-2cm}
\includegraphics[width=4cm]{tex.jpg}
\end{flushright}
Set of Slides boardening the talk (nobody had questions, time for more slides).
\end{frame}

\end{document}