Could you do it so BBCode is parsed in the custom fields? For example, if a custom field called "photo" is created and a user adds [img]http://www.link_to_photo/photo.jpg[/img] a photo is shown instead of the code.
Not sure how hard this would be to do, but it would work like a charm in my case...others I'm sure wouldn't mind it either
EDIT: This btw is one of the most useful hacks for me ! Thanks