Like Lukas said, swapping the tank for a lighter plastic tank under the seat, slimming down the trellis frame, replacing the swingarm (I have both a 950 and RFS swingarm on my project bikes and the RFS is WAY lighter) running a standard PDS shock instead of the 950 with preload, smaller rims, spokes and hubs, lighter braking components, minimal fairing and bodywork (make the tank the rear fairing, carbon fiber skidplate, exhaust would have to be done by consumer to a single carbon can due to EPA, lighter motor.
I still don't see how you could get that to 350 though. with all the stuff guys want on their ADV bikes. Possible but I think it would be a real stretch.
Is it that much different from the 950SE to warrant a new bike and engine? Probably not with the 690 in there.
We're not out here to rough it. We're here to smooth it. Things are rough enough in town.