I normally just throw all of my cash (generally ~20) at him and then move on when I get outbid.
If you think one person will outbid you by a lot, and if you really want to get crafty you can try this: say you have 24M and the other guy has 27. start off bidding like 20M and then if/when you get outbid wait maybe a day and a half (or maybe two days? IFA signing schedules are sorta random). then dump all of the 24M, and if you do it at the right time and the other guy is bidding say 23, he might sign with you before giving the other dude a shot to counter.
this strategy is going to succeed a low % of the time, but it could be worth it if somebody is trying to save a wad of cash and you time it right.