Talked to the RYCA folks yesterday. The way they do it is basically what I was doing-remove the shock, and set the belt tension at what will be the tightest point in the swingarm travel. This means the belt is pretty floppy at full extension, but they say that isn't a problem.
Looked a Buell yesterday. They use a fixed, large diameter roller under the bottom of the belt. I guess the theory is that as the s/a moves up, belt tension increases, so there is no need for a spring loaded tensioner.
I'll try it as RYCA said. They've certainly built enough bikes with longer shocks, and if they haven't had a problem, it must be OK.
And I'd hate to add a bunch of gak to the nice clean lines of the bike.

I think Dave  is right,loose on our bikes can't really do damage ,there are bikes like the yamy 1700 roadstar,bolt R-spec 942 and BMW 800,running 90+hp with no idler pulley on much thinner belts.I don't see why our bikes even with motors built to the max (45hp?) can't handle the load on an even wider belt that is stronger than chain.The belts are built of fibers that that don't stretch ,we can only cause damage by over tightening .

Armen , It is about hp! If you snap the throttle closed the sloop in your belt moves to the top side due to the rear wheel moving faster than the drive pulley,now snap the throttle back open and you have belt /chain snatch,a lot more with higher hp,but the savage doesn't have it.