Setting \itemindent
for a new itemize environment solves the problem:
\newenvironment{beameritemize}
{ \begin{itemize}
\setlength{\itemsep}{1.5ex}
\setlength{\parskip}{0pt}
\setlength{\parsep}{0pt}
\addtolength{\itemindent}{-2em} }
{ \end{itemize} }