You have to:
1. Modify the Air Tasking Order on the fly. Not easy, but it can be done--but it takes time.
2. Get a jet with the right ordnance. Time's a-wastin'.
3. Get said jet over the target. We generally do not have jets flying around in circles over all of Afghanistan, burning lots of jet fuel, just in case a good target comes up.
4. Do all this before the imam running the funeral says the equivalent of "Th-th-th-that's all folks!" and the group breaks up. Notice that the imam and the funeral attendees understand that a big crowd of 'em gathered in one place is just BEGGING for a smart bomb or two, so they're either done very quickly, or they're dead.