Go custom. I'd hit E46fanatics.com, as you'll hear from many 3 series owners who've gone with many different companies to get widebodies done (or did it themselves, with DYI's the whle process through). Some good, some bad.
Sedan's are especially hard to get widebodies done on (not harder, just rarer) - but I've seen some HOT photos over there of a few that had me drooling.