In all the interviews i have been in, and all the ones i've interviewed people for, never once have they written down anything that i/the candidate say to the "any questions?" question.
So in my opinion, dont feel pressure to ask something for the sake of it, you are more likely too goof! Only ask a question, if there is something about the role, or the company you want to know that hasnt been covered, i.e how big is the team, do you anticipate any opportunites for training on the job, will the role be based entirely at XX place or will it involve any travel?
The only other option, is to use the opportunity to sell yourself or your enthusiasm for the job one last time, maybe something like, "No, i dont have anything else to ask, everything is covered, and i think the role sounds really interesting (if poss, name one of your skills and one key point about the role which uses it) and thank you for the opportunity to come and meet you"
Good luck tomorrow, and keep us poseted as to the result!
K