\documentclass{article}

\newlength\colSep
\settowidth\colSep{\kern1em=\kern1em}
\def\specialLine#1{\multicolumn{2}{c}{%
		\array{@{}r@{\hspace{\colSep}}l}#1\endarray%
	}}
\begin{document}

\[
\begin{array}{r@{\kern1em=\kern1em}l}
    x & y\\
    y & z\\
	\specialLine{u & v}\\
    \textrm{and} & \textrm{so on}
\end{array}
\]

\end{document}
