The first thing you should do is buy a copy of John Hermann's "Motorcycle Adventures in the Alps". Then buy the Michelin map for the Alps. Use Hermann's book to guide you in marking off roads to try.
If you have riders that are not good in the tight stuff, there are lower pass roads that are not as demanding.
Many BMW dealers in Europe rent bikes. But it isn't cheap -- I've been seeing prices in the $150/day range, and that's with a 200 or 300km limit (additional kms cost about €0.50, which can add up fast).
The best prices I know of are from Stefan Knopf (
www.knopftours.com), but he's in Heidelberg. Heidelberg is a one hour train or bus ride from Frankfurt airport, and it's about a 3 hour ride from there to Zurich.
And if you don't want to play in the Alps, why are you going into Switzerland? It's the most expensive country in Europe. Stay in Germany or France to get better value. You can have a great time riding in the Black Forest or the Eifel (area west of Cologne) in Germany or Provence in France, for example.