When DF users come in contact with sea stones most of their energy is drained. So they'r really weak. I doubt that he could control the other part which is out of the cell properly in order to escape.
… well if ALL of his parts gets pushed through the bars there arent any bars seperating him and his parts so why wouldnt he be able to controll them anymore?
(but going by your assumption that he opnly pushes a hand or something through to get the keys to his cell: why would he be touching the seastone after some of his parts are through?)
@Ivotas:
While I don't think that this could happen the general idea is brilliant.
Why couldn't this happen… I think there are some assumptions floating around that I'm not aware of...
Did Luffy stop being elastic when he touched the seastone cage in rain diners? I don't recall...
@tigerlily:
this raises a question for me: can he actively control his powers while in a seastone cell? Does he bleed when he's stabbed in a cell or are his powers still active and he falls into pieces?
No matter how it turns out, I'm pretty sure Buggy's escape will big a gigantic Comic relief XD
As far as I recall Luffy wasn't affected by the rain diners cell untill he directly touched the bars.