just to basically say I was just in the same predicament and my solution is working out so far.
I am using the rear Cortech sport tailbag on my tank... it's perfect for my S4R. It's wide enough for my 17" laptop when expanded but not too tall. I hook the two front bungees to the two thinner bars in the frame up front near the steering column and the two rear bungees hook under the tank. I've had no damage to the paint so far. It's nice having my equipment on the tank verses the tail. I'm very happy to get my gear off my back, especially in the summer.
I presume you're set by now but if anyone else comes across this hopefully this helps!