I think the "feeler" bet is probably your best option. Bet about half the pot and see what happens. Since he's the chip leader, if he has ace-anything he'll probably call your push. But if you bet out half the pot you are not only giving yourself a chance to fold if he comes over the top, but if he just calls it with ace-small you are getting to see the turn the cheapest way possible probably. This gives you a chance to hit your set or a backdoor straight.