If you are correct about the concrete steps being precast, and I'm guessing you are, that may be a possibility if the void is accessible.
I still haven't heard from them, so I don't have any more information yet. As I had told my brother-in-law if they had used pesticides to try and get rid of them, I really wasn't interested. So now I will have to wait and see if they call. If they do call I now have a much better list of questions to ask.
Even if they never call, what I gained from your replies and from my research into trapping out bees has given me a far better understanding of what it takes.
Probably the biggest thing I didn't understand was the unlikelihood of capturing the queen.