I have a bunch of 4130 chrome moly plate and bar stock lying around from various aviation projects, and a MIG welder. I figured it would be too difficult and expensive to recreate the parts shown in the photo, but I'm comfortable welding and fabricating.
I committed myself to the project by cutting the messed-up ears off my frame and filing the remains off. Cut out some rectangles out of 1/8" steel plate and commenced to cold-forming them (AKA beating the crap out of them with a hand sledge) until they conformed to the shape of the frame. Turned some spacers out of 3/4" round stock on my lathe, to mimic the cylindrical part of the now-removed tabs. Cut some tabs and bits out of more 1/8" flat stock to create new ears.
I was originally planning to through-bolt the tabs I was fabricating to the frame, but I realized that the airbox was in the way, and there was no way to solve that other than unbolting the entire frame. Which I didn't feel like doing. So drilled 3 holes per side and tapped them for M6 fasteners.
Used a bottle jack between rear tire and bottom of seat pan to get the rear subframe located correctly, then tack-welded the now-bolted plates and tabs together. Finish-welded them off the bike, painted with some zinc primer and voila.
They are now secured with 3 M6 screws per side, with a little red Loctite on the threads for good measure. For the first time in the 12 years I've owned my R1100S the tupperware and saddle fit correctly. It may be the placebo effect but the saddle feels more comfortable as well.
Some photos (welds are ugly but they won't break):
