That said, does anyone have first hand knowledge of a 5-spoke front wheel that will fit the R1100RT?
I do not.
I'm replying to this message only because I see that nobody else has yet.
There is no ME-880 fitment for a K1200RS. Do you mean that you have a K1200LT rim?
Anything can be made to fit anything. But is this project a good idea? Perhaps you would be better off researching the available fitments for your bike, then choose the longest-lasting tire?