User blog comment:Blackendedsoul/Unique Gomu Gomu/@comment-4800978-20120301052840/@comment-4800978-20120301061207

Well, it's not like Luffy can willingly stretch his head either - he'd need that outside force to alter his body. I also just recalled a moment when he was in seastone - Loguetown. But that doesn't really prove anything other then Buggy can't willingly use his abilities under the influence of seastone - same as all other DF users.