I'm pretty sure you only have to spend your junior or your senior year at Hershey, not both. I think they ask you which you'd prefer, but they can't guarantee that they can send you during the year you want.
The only ways to get out of it is if you're in ROTC, blue band, a certain sport, or Schreyers (there may be a couple scenarios I'm forgetting). You can also get out of it if you find someone else in the nursing program that would swap with you, so you'd do 2 years at UP and they'd do 2 years in Hershey.
Honestly though, I would go to Hershey if I were you. Back when I was considering PSU's Nursing School, I really did not want to have to leave UP for one year, but in the long run I knew it would be worth it if I wanted to be the best nurse I could be. You're just not going to see the kind of exciting cases and gain the kind of experience in State College as you would in Hershey. In the end, you're going to college to gain a good education, and when it comes to nursing, first hand experience is a big part of that.