Dennis: I have used the Sitlight pad from Gossamer gear with great success. Not only will it work as a pack frame, its a sit pad, a freezer bag cozy, and a fire fanner.
The Sitlight pad costs about $7 and weighs a mere 1.3 ounces.
Put the corrugated (egg crate) side towards your back.
I also have the original 1/4 pad that came with that pack, which I just realized i failed to send w/ the Jam2. But, without the pad sleeve it really wont help much in the way of stabilizing a load or padding your back. Especially tho, it wasnt made to stabilize a load anyway and its just a redundancy on GoLight's part and a useless extra weight if you ask me (and many others)
I did the rolled pad thing too and found it is not comfortable. For starters, the Jam is not a perfect cylinder. It is smaller circumference at the top and much wider at the bottom. Use the sitlight. It will conform to your back quite nicely and help maintain pack shape even with 20+lb loads. hold the ridgerest in place with the two longer side compression straps. I left them long for just this reason.