I use the po'boy throw levers on some scopes.
Buy the universal coaster here, you get 2 in the package.
Coasters | Breakaway Tackle & Development
They are not pretty, but they work.
For metal zoom rings, I cut a little strip of innertube (rubber band will do, too) between the coaster and the zoom ring; this also eliminates the possibility of bitching up the finish on the scope.
Joe
edit; here's a picture I found on the interweb of a po'boy throw lever installed