I have a 2004 made in 2003 GS adv that is twin sparked with super servo assisted abs brakes.
I have also purchased used wheels off a r11xx gs, for off road use.
To make the necessary changes, I purchased the correct (used) rotors and a new abs ring that is meant for the 2004.
Then filed a flat spot so as not to interfere with the new abs ring.
I see that you have a R1100GS, can't give you a clear answer but I wrote this up and went out and take the picture, so I hope this helps someone.
I think the problem will be mounting the abs ring.