I'm pleased to announce the first public version of my pygtk app Gwinwrap. It's still very new, and most likely buggy, but if you feel like trying it the code is at Google Code.
Basically, it finds all your xscreensavers and lists them, with a preview. You can choose to start the xwinwrap screen with opacity, and choose whether or not to use a nice command before for better cpu management. Xscreensaver Arguments are also accepted in the input box.
Hope you like it!