[pmwiki-users] Compute $EditRedirectFmt?

[Lucian Wischik]

I'm trying to use $EditRedirectFmt. The documentation
  http://www.pmwiki.org/wiki/PmWiki/EditVariables#EditRedirectFmt
suggests examples like
  $EditRedirectFmt = '{$Group}.HomePage';

But I want $EditRedirectFmt to be computed through a regexp on
the $FullName. For example, if the user was editing a page
"Main/TopicComments" then I want to redirect to "Main/Topic".
(i.e. stripping "Comments" off the end).

It looks like $EditRedirectFmt can't be used in this way. That's
because it merely gets substituted by the FmtPageName function.
I guess I could alter pmwiki.php myself to get the desired effect,
but I want to confine myself to local changes.

Am I wrong? Is it possible somehow to use $EditRedirectFmt as I wish?

Thanks in advance for any help,

-- 
Lucian