I can't think of any product which would take out the bees, without harming the mantis.
If you can find the hole, you may want to try using a gopher gaser, (a smoke bomb, that pushes smoke with a high sulfur content into the hole) that may chase them out and away, but I would not waste any time getting it into the hole, and getting away from the spot!
I found one of those nests on time while weeding my mom's strawberry patch. I grabbed a hold of a clump of grass, and yanked out the stinking nest! I think they stopped counting at 40 or 50 stings. My arm was completely covered by them, from finger tips to elbow!
You could try blasting some Shoo Fly or Raid wasp and bee killer directly into the hole. That would give you a much smaller area contaminated by the insecticide, but any mantis that comes in contact with it would still die.
Another idea would be to put a bee trap close by, and hope you get them all.
What ever course you take make sure you do it at night! That way you won't be getting nailed from behind form those bees returning to the nest.