Frank is right, that was a problem in the making quite a while ago. I had a similar crack with another gusset further back on the submframe. I caught it before it could stress the tubing and crack it.
Mitch, the pieces you speak of are for the R1100GS's where the subframe mounts to the transmission. This doesn't apply to the airheads, but I highly recommend it for the affected bikes.
Rubber Cow's suggested fix is the best one, if you have the guts to cut up your subframe.
"I don't know what you do, but I know what I do, and I don't do that." --Uncle Doug, R.I.P.
"Without the possibility of death, adventure is not possible"--Reinhold Messner