User blog comment:AYET/Talk about chapter 716 and episode 604/@comment-4754162-20130802053455/@comment-13876472-20130802080743

As far as I understand the Jake Jake no Mi and devil fruits in general, they are abilities of user's body. For example, Jake Jake no Mi on Robin gonna result almost the same as if Law casts "Shambles" on Kelly and Robin.

In the shambles case, Kelly would have the possibility to use Hana Hana no Mi, but with troubles as Kelly himself is not profficient on using it (like Franky on Chopper's body using Monster Point). The difference would be that instead of having Robin's skin and face, we would see Kelly's face, tatoos and skin generally covering Robin's sillouette.

Even with the current use of Jake Jake no Mi, we can see somekind of stretch on Kelly's body, since he had to cover his brother's bigger surface. In the end, it is a traditional fashion on manga series to use ...endurant clothes that can be manipulated by the user's changes in shape, size and form. Just like Akainu's clothes didn't get burnt while he was in his Magu Magu form and Luffy's clothes can "follow" him during Fussen, that "Kelly Jacket" could stretch on Luffy or become elemement on the logia users.

The only problem I can see on it is the fact that practically we are speaking about two fruits co-existing on the same body, so I'm wondering if Kelly, as long as the guy who wore Kelly, would explode. Although, as they are actually two individual bodies (acting as one) I doubt that we would have such a problem.