[D&D 3.5] How do I work this insanity?

Sir Red of the Manti

So essentially there's a halfling barbarian in my party who's decided to ride on my human fighter. In combat, we've decided that we want to be able to chuck the barbarian ten feet behind our target while charging, then have the fighter improve bull rush the target into a pair of flanked attack of opportunities from each of us. My question is, what's the best way to get the halfling off in the middle of a charge, and what sort of die roles are going to be involved in pulling that maneuver off? Also, is there anywhere specific I should be looking rules wise on having characters ride other characters?

delroland

There's a 3.5 feat called "Fling Ally" (in Races of Stone, I believe). Unfortunately, throwing the halfling would chew up the fighter's attack for the round (so no charge or bull rush), and knockbacks don't provoke AoO's.