I had this problem.
Rode a Felt F-65 and wanted to do some supported touring or light loaded touring
quizzed dozens of riders for ideas.
Visited some yahoo group dedicated to ultra light touring
(even exchanged notes with a fellow who toured with the same bike and some post mounted rack and lots of plastic bags and space blankets)
in the end, this is how i resolved the issue:
I got a bike with rack mounts and other braze ons