Well, I finally did it… sawed off about 4″ of my stock Bonneville rear fender. Here are the results.
The procedure I followed was to trace the existing curve of the stock fender onto some flexible cardboard. Then I cut out that curve and used the cardboard for duplicating the curved line about 4″ higher than the stock fender, eliminating the reflector, but still coming down lower than the stock license plate position.
I used flexible pin striping tape to create a line on the surface of the fender to follow. I used a 4-1/2″ Heavy Duty Angle Grinder from Harbor Freight Tools to do the initial cut, then used it to clean up the final shape. Hand filing was the last thing before touching up the edge with black paint and then remounting the fender.
March 16, 2014 Update
In keeping with the repainting and finishing I am doing on the rest of the bike, I removed the fender yesterday and have prepped it for refinishing with Performix Plasti Dip, black.