I had this problem with my S&S bike, and I solved it by using a seat-post-mounted rack. Mine is a Topeak rack with optional side panels (https://www.topeak.com/us/en/product...ual-side-frame). It works, but it's not ideal. You have to be careful not to overload it, and even when not overloaded, it doesn't seem the best way to carry any amount of gear. But with a small enough amount of gear, it does the job and packs easily. Still, if you can pare your gear down enough, a seat bag would be a lighter option, and if you need/want to carry more than goes in a seat bag, then I thing some of the folding options already mentioned would be better. I like my seatpost-mounted rack for ease of packing and ease of set-up, but for sturdiness, I've been considering something along the lines of the foldit.