I have had 3 different XB's with chain drive. Two of them I did myself and one was done previously to me owning this POS whipped on poor track bike, as well as several engine mods to it. I'm not even sure of all the engine mods, but it was the fastest XB I've ridden. Dang thing would power wheelie in fourth gear if you yanked on the bars

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I was nervous about the lack of a cush drive as well and kept a close eye on the rear sprocket mounting bolts. I don't know how many miles that rear wheel had on it, compared to the bike (because race bike), but I never had an issue with the bolts wobbling out the holes. I did give them and extra 10lb/ft when I'd torque them in pattern. Never had a problem even on track days.
EricZ made his own final cush-drive for his amazing turbo bike:
http://www.badweatherbikers.com/buell/messages/32777/733678.html?1394589182
Lunatic is right, there is a little spring set up in the stock clutch basket, but thats for the primary assembly and chain. You're worried about shock loading the whole final drive and transmission. A slipper clutch may help throttle transitions from on to off the gas, still not helping shock-loading, and they are ridiculously expensive. The EBR one used to be about $1000, and the STM one is junk and needs constant adjustment and maintenance (IMO).
EricZ also had a great idea and made a primary cover that fit an XB,
but used an 1125 hydraulic clutch assembly. Slipper action, hydro slave, he's awesome:
There's a better link somewhere:
http://streetfighterperformance.com/xb12-turbo/drivetrain/clutch