It depends on which one. I have fit a Jazz ashtray over a Badass II before but I know that the P-bass ashtrays won't fit over them. At
www.basspartsresource.com used to have oversized P-bass ashtrays that would, but I no longer see them on the site. Maybe if you troll around on ebay long enough you could find one of the oversized ones. I hope this helps. Have a good one!
-Joe P.