If you have a copy of the sixth book in the legacy of fire AP, it has a sidebar about cinematic combat. in a nutshell, each player makes a skill check each turn... using their sword, casting spells, channeling energy, whatever. if they succeed, a number of enemies die, if they fail, they take damage from the swarm of monsters. its been years since i even opened that book, but i think it'd be worth a look into.
conversely, you could set it up as something completely different. use the chase scene rules from the game masters guide and set up a series of events that happen during the battle, and require skill checks or attack rolls or whatnot for them to go as planned. then have some back up events if they screw up enough times, so that this doesn't become a TPK.
or you could just have a ton of minis on the map... its really fun, and the pcs feel satisfied when their fireball kills like thirty.
anyway, there's my two bits. i hope it helps.