I needed about a half inch more clearance between the stays if I had any hope of fitting a 3-inch tire. After mulling over some ideas of cutting, spreading and reinforcing the stays I decided to give this a try.
By rearranging the hooks and nuts, a cheap set of Harbor Freight coil spring compressors can be used to spread the rear stays. I used them in tandem so that the hooks interlock. It actually didn't take a lot torque to do the work and in about an hour I had my half inch!
(note: just be sure to brace the rear dropouts so they don't spread)