any chance you can get the rest of the stump cut so that you can just take it home and take your time? sounds like it's in a bad spot and begging to be sprayed?
also wonder if you can get access to the bottom of the hive maybe through a larger drilled hole. then either smoke the crap out of them to move them up, or use something like bee quick? just to be on the safe side, unless you are pretty sure you know the size you are dealing with, i'd lean toward putting a couple of boxes on there until you get them off. you can reduce later.
if you can drive the queen into the box, most of the rest should follow. then you can just chop into the stump and retrieve comb is you want to. less mess if there is public around.
make sure you use some drawn comb. queen might be more cooperative if you get her on some right off the bat.
that's all i can think of for the moment :)