LaTeX.org

Hi,
I achieve what you were trying to do by changing the Stefan's code as:

\newenvironment<>{varblock}[2][\textwidth]{
\begin{center}
\begin{minipage}{#1}
\setlength{\textwidth}{#1}
\begin{actionenv}#3
\def\insertblocktitle{#2}
\par
\usebeamertemplate{block begin}}
{\par ...