4th button

[Silverthorn]

Relating AI, this is like hell-moves: the computer will never execute these moves. LF2 was programmed for three action-keys. Everything is dependent on them. Attack is for attacking (duh!), answering a dialog-box, increasing values (in battle). Jump for jumping (to state the obvious, second duh!), going back in menus, decreasing values. Defend for (no, I won't mention defending :P) starting a special attack, and increasing values faster.
AI has been programmed to make use of these three keys (plus directions, of course). It won't know that there's a fourth possibility. Would suck, IMO.

Well, you could decompile the game, learn C++, and do it yourself

If that was possible......... :P

but 4th button need for mooving between 3 fingers (cuz using 4 fingers uncomfortable)

Really? I have no problem using 4 fingers

But yea, Silva refuses to do it (for obvious reasons (yes, I had to borrow that slogan^^)), so bury your dream :P