Spoke protectors are designed specifically for the spoke count of your wheels and tooth count of your largest cog. They shouldn't affect a cassette's positioning on the free hub shell if properly selected. That is the way it is on nonretro bikes at least.

Loosescrews.com sells them.

http://www.thethirdhand.com/index.cgi

You can do a search on spoke protectors and a variety will pop up.

A2, I didn't try a search on dork disks.