OK, got off the Phone with FMF, and Pro circuit this morning.
 I was asking them on silencer isolation bushings,  reason for calling them was to look for a low cost insulator for some of these aftermarket silencers, they both agreed to use OEM if available or fits, if not use a 0.125" Thk rubber washers and 8mm ID fender washers sandwiched on the silencer would work, preferred would be a some kind of metal bushing (OEM is 8mm ID x 12MM OD x 17mm) or use a partial threaded bolt  (Un-threaded 17mm shoulder)
seems easy, plus an easy trip to your local hardware store.
Unless we  can get SBLT500R to make some nice custom ones?
Bolt / Rubber Washer / Fender Washer

With the OEM bushing

Use a dab of Blue #242 Locktight