% upLaTeX document
\documentclass[uplatex,a4paper]{jsarticle}
\usepackage{bxjalipsum}
\usepackage{plext}% for '\bou' command
%!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! TeX code BEGIN
% with a bit of TeXnique...
%% Expand 'em all!!
\edef\wagahaiOne{\jalipsum[1]{wagahai}}
\edef\wagahaiTwo{\jalipsum[2-5]{wagahai}}
%% \argexpd\CMD{<argument>}
\def\argexpd#1{\expandafter#1\expandafter}
%!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! TeX code END
\begin{document}

% rather nonsensical examples
% (The \bou command add "bouten" to the given text.)

\argexpd\bou{\jalipsumiroha}

\argexpd\bou{\wagahaiOne}

% NB. The meaning of \wagahaiTwo contains \par, so it is
% not suitable for \bou.

\end{document}