Send them a rejection letter so they know how it feels:
Dear Admissions Committee,
It is my sincere regret that I must inform you that after much consideration of your school's credentials and mission, I have decided not to matriculate to the College of Osteopathic Medicine.
This has been an unusual year for me, and I have received a record number of acceptances. With so many great Osteopathic Medical Schools that have accepted me, I can only choose to attend one. Each of these schools offers something special and unique, and in the end, I faced a very tough decision deciding on which school I wanted to attend.
Although you may be disappointed, it is my wish that you find success and fulfillment in teaching Osteopathic Medicine to other bright and wonderful students. I thank you once again for taking the time to accept me, and I wish your school the best in your future endeavors.
Sincerely,
Superman DO