Pre-fill CVS/SVN -any VCS- commit message?

Is there anyway from a plugin, to automatically pre-fill the current VCS's
commit dialog with content?

i.e. In my JIRA plugin, I'd like to prefill the commit dialog with a
standard string mentioning with issues had been worked on during the
commit etc.

Is that possible?

Or taking it further, is it possible to add a JPanel to the commit dialog,
and have some code run before/after commit to do additional processing, or
modify the commit message depending on something in your panel?