be able to provide arbitrary parameters to the maven release command line. (not
merely versions like today).

Suggestion:
Configure it like release:prepare release:perform -Dusername=%USERNAME%
-Dpassword=%PASSWORD% -DreleaseVersion=%RELEASEVERSION%
-DdevelopmentVersion=%DEVELOPMENTVERSOIN% - or some other type of placeholders.
This should lead you into a dialogue where you're prompted for username, pw, rel
ver, and dev. ver for the release.

This way you won't have to hardcode credentials into the hudson job configuration.