Honestly, I think your classes that teach people how to work in a band environment is very unique (I only know of one studio in a few hour radius of me that does such a thing)
If you could get clearance to use your parking lot (maybe work out a co-advertising deal with food vendor in the same lot) and put on a free concert, cycling in different acts of different ages and abilities.... the participants and their friends/family would create a decent sized crowd before anyone new shows up (always a killer when the crowd is thin) and could really distinguish your school because of the wide range of instruction (you still have vocal teachers, right? )
I know that when I worked for a Gym, we would do holiday demos and would rack up huge numbers of lessons, particularly from families looking for something fun to do during the cold holiday vacation. I know you guys don't have the weather issue, but Parents might buy lessons for their kids to get them away from the Wii for the Holiday break.