I'm using memoir for a large document and want to center the toc entries corresponding to parts (page entries are turned off). I read the manual (specifically pp. 161-166) and while I have no problem adjusting the positions of the part number or title separately, I can't figure out how to center the part number and the title together as a whole. The MWE that demonstrates this is as follows:
\documentclass{memoir}
\cftpagenumbersoff{part}
\begin{document}
\tableofcontents*
\part{Part A}
\chapter{Chapter a}
\end{document}
To be more specific, I would like "I Part A" to be horizontally centered. If there were a second part called "B", I would like that to be centered like "II Part B".

\@tocrmarg(dafault value of2.55em) reserved to typeset the page numbers for other sectional units using some extra space; you can change this by adding\hspace*{2.55em}just before the first\hfils in my example code above. – Gonzalo Medina Nov 28 '11 at 21:15\hspace*{\@tocrmarg}(instead of\hspace*{2.55em}): that way, one needn't even look up the value of this parameter. :-) – Mico Nov 28 '11 at 22:36