\documentclass{article} 
\usepackage{fancybox,framed}
\textheight=7.5cm% only for demo
\makeatletter
\renewenvironment{shadow}{%
  \def\FrameCommand{%
    % \setlength{\fboxrule}{\FrameRule}%
    % \setlength{\fboxsep}{\FrameSep}%
    \shadowbox
  }%
  \fram@d{\advance\hsize-\width}%
}{%
  \endfram@d
}
\makeatother
\newcommand\x{text-gfdjh-dfajh fbv-fbv.bfvjfhglgk jhälgskj}
\begin{document}
\begin{shadow}
\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x\x
\end{shadow}
\end{document} 