How do I delete values from the debconf database?

Per this question I've now got wonky preseed values for my gitolite installations such that gitolite fails to install. I need to clear my debconf database of a few keys, but I see no way to accomplish this. Neither did this fellow, as near as I can tell.

Is it possible to clear the debconf database of a few values?

echo PURGE | debconf-communicate packagename

This will remove ALL the config for this package, so if you want to save some, get them first with debconf-get-selections, then replace the ones you wanted to keep.

You can find all possible actions in the Debian packaging manual. Instead of purging all question of a particular package you can try

echo RESET question | debconf-communicate packagename

or

echo UNREGISTER question | debconf-communicate packagename