I checked around the forums, and nobody had posted anything about this yet so I'm making a thread. The actual idea was IceeDesertEagle's, just to give him credit.
We started out boosting dead rock, killing everything we could in the tornado. We got to wave 20 without too much trouble but we came about 2,000 shy of the 50,000 score. Rather than letting ourselves die so we could try again on the next wave (and possibly come up shy again) we left the SECOND to the last guy alive. The last enemy to spawn in a wave is ALWAYS alone and a team challenge, so you can kill off every enemy until theres 2 left, but only one spawned.
Every time an enemy downs you and you get revived, the person reviving gets 50 points. Not much, I know, but if you come up a small ammount shy, it's better than trying to play the wave 5+ more times hoping you'll get it to pop.
So we sat there and let the enemy down us, and kept reviving. It only took about 20 minutes or so to get the rest of the total we needed and no need to repeat the wave