%%
%% http://tex.stackexchange.com/questions/16003/phantom-and-line-break
%%
\documentclass{jarticle}
\usepackage[normalem]{ulem}

\makeatletter
\def\UL@putbox{\ifx\UL@start\@empty \else % not inner
  \vrule\@width\z@ \LA@penalty\@M
  {\UL@skip\wd\UL@box \UL@leaders \kern-\UL@skip}%
    \phantom{\box\UL@box}%
  \fi}
\makeatother

\begin{document}

Some text \uline{some text to complete some  text to complete
some  text to complete some  text to complete some  text to complete some    text
to complete some  text to complete} some more text.

色は匂へど\uline{散りぬるを我が世誰ぞつねならむ 有為の奥山 今日越えて 浅き 夢見じ 酔ひもせ}ず

色は匂へど 散りぬるを 我が世誰ぞつねならむ 有為の奥山 今日越えて 浅き夢見じ 酔ひもせず


\end{document}
