Haha, Tetris' suggestion might actually work the best.
Here's an update:
He finally responded to my emails on Monday saying he'd have it in (to Princeton Career Services, they're the ones sending all my letters out) by Tuesday. But when I called Career Services today (Friday), they said it never came in.
I think I'm ready to give up. Like someone said above, its probably not a good sign for the quality of the rec that he's dragging his feet like this. I'm just going to have the 2 recs that are already in sent out.
Without his, I only have 1 academic rec, and 1 work rec. I'd definitely prefer to have 2 academic, but it doesn't look like its going to happen.
I think I'm also going to call up schools and tell them to consider my file complete once the two get there. If the 3rd one gets there before they read my file, great, but I don't want it holding it up.