I took a few moments to consult on this problem with the Special Needs Counselor here on campus. She agreed that this is a "real tuffy". Here is a summary of our discussion:

It is standard operating procedure in many auditoriums and concert halls to allow front-row-center seating for the physically challenged. This is partly to aid some of the sight impaired folks but also because many halls don't have anywhere else for wheelchair-bound people to sit. Armed with this knowledge, it would probably be wise to inquire before a show whether such accommodations have been made. This would at least eliminate the "Surprise!" aspect. If it is still seen as a potential problem, then perhaps the person in charge of the show could be persuaded to move the reserved seating for the group to a spot in the middle where they might not be quite so distracting (at least, to the performer). An explanation or even a retelling of the story above might help to overcome objections which might be voiced.

It would seem that for this, forewarned is forearmed to some degree.