The only guesstimate that I can make on what spring rate is off this forum because of the odd set-up.
Sounds like Cannon Racecraft is the way to go.What is your weight?
it's not really an odd setup, it's just a better direct mounted shock. i used a spring rate that was close to the oem spring rate because i had a lot of miles on the versys shock and that spring worked pretty well when the bike was loaded. if you were not loaded down with gear or passenger, then a different rate might work better. i do remember guys trying to set up that group buy Elka shock, and many felt the supplied spring was too heavy, although there was no consensus on the exact oem rate as tested, therefore no real good baseline.
if you go with Cannon, i think you'll find that they're easy to work with.
i probably have 400# on the bike in travel mode.
a note on prepping the R1 for installation...the bushings on the R1 need to be bored to the diameter of your oem shock mount bolts, a nominal 12mm. you do not want any slop in either end. the SS needle bearing end needs to be bored because it's hardened, while the conventional end can be drilled, but only if done carefully. i made a small fixture to position the conventional shock bushing and hold it in alignment to be drilled. it's just mild steel, not hardened. you can job this task to a machine shop, target price for both ends would be $25-30. take a mounting bolt with you so they can check the diameter and do a proper setup.
not all R1 shocks are the same, so know what you're buying.
even with a custom spring and a little machine work, the R1 is looking more and more like a real nice low effort/low cost mod for these bikes. my stock 2008 R1 looked like new for a purchase price of $25, so even with postage you should be ready to mount this shock for around $200 complete. compare at $5-600 and up for the big boys.
thanks to the guys who did the initial homework on this shock.