What to Isorate With?

[toss]

MP1 in this hand looks at something like 98/63/1. He looks at nearly every flop, raises and 3-bets PF like a mofo, but is surprisingly passive Postflop. This means he'll call down with usually nothing. He'll sometimes bet or raise bet with weak hands, but he's easy to control.

My question is whether I can isolate with A4s? Keep in mind the others players at the table will probably suspect you of isolating especially the Big Blind whos like almost as worse as MP1.

Party Poker 10/20 Hold'em (9 max, 9 handed) converter

Preflop: Hero is MP3 with 4[img]/images/graemlins/heart.gif[/img], A[img]/images/graemlins/heart.gif[/img].
<font color="#666666">1 fold</font>, UTG+1 calls, <font color="#CC3333">MP1 raises</font>, <font color="#666666">1 fold</font>, ...Hero does what?