Try the slash and sun on a cold night.

The chemicals should break down with time.

Thanks for the idea. Cold night! I'm hoping to have access to the compost before Halloween, but it might not happen. We slashed and ran last night and the bees were still very unhappy this morning--actually it was dreadful--they acted like earthquake survivors searching the rubble. No no do NOT anthropormophize!

Please be sure they are NOT honey bees looking for new colony. I understand there is something going on that is hurting the population and a result is the lack of pollination, which means no fruit, etc...
Last year I had a "cone" of bees descend on a small tree:

That's an amazing picture!!!

No, they are not honey bees--I would leave them if they were and do without my compost! I do have honey bees in my garden, but I don't know where that nest is. These are bumblebees and have been in the compost for at least two years. My husband borrowed a chipper shredder to chew up our huge pile of brush and hit the nest just under the rough stuff in the good stuff that's ready to use. I'm not sure, but they may have left now.

As you may have already discovered, just disturbing the nest may be enough to make them look for another home. It's a shame though, as bumblebees are harmless (they do have a nasty sting but are generally quite reluctant to use it). I'm assuming these are NOT yellowjackets, which nest in similar places but are much nastier and more aggressive.

I still remember the bumblebee sting I got when, at age 4, I "wanted to see if they felt fuzzy too!" But I still love them, and all the varieties of fuzzy and not-so-fuzzy bees, wasps, flies, beetles, etc., that are buzzing around the allysums and coriander and whatever else is blooming, pollinating my cucumbers and zukes and tomatoes and peppers, and helping to keep the aphids and caterpillars down to manageable numbers. I think my garden would be fine without the honeybees, who seem to be single-mindedly focused on the clover right now. I hope your humble bumbles find a new home!

I had the exact same problem, and got stung (2 per ear, both ears) when I tried to pitchfork the mulch and the bumblebee nest, accidentally. The sting, even all four of them collectively, was not bad at all. The bumblebees moved on, because the next time I checked, they were nowhere to be found.

Gardeners,
Please don't persecute bumblebees. They too pollinate your plants, and do so for longer and at lower temperatures than honeybees. Also, many bumblebee species are experiencing mysterious declines that parellel that of the honeybee.

If you have bees in your compost pile, consider yourself lucky, and start a new pile somewhere else!