Originally Posted by pacificcyclist

The only way to do this is to use a rack like the Axiom Streamliner DLX (cheapest) or the Tubus Fly (more expensive but lighter). The attachment point for these racks are on the QR rear axle and the caliper brake bridge. You'll have to remove the rear caliper brake to install the single stay and then re-install it back. You may need a longer recess bolt, but I managed just fine with the one on my Trek 5000 carbon bike. The maximum I would tour with a carbon bike with these 2 racks would be 20lbs -- less would be best and can be done camping wise. With a Old Man Mountain rack which is the creme de la creme in this rack category, you can push it to 30lbs. I had the Streamliner DLX before, but now using the Old Man Mountain rack as it's more secure and is secured via the brake bridge as well. However, I fashioned one of the long seat stays to work on the bridge.

In regards to seat stays. According the Old Man Mountain, the full weight of the load is borne on the rear axle mount leaving the stays as stabilizer to prevent the rack from rotating from the axle axis forward during breaking or steep downhill descent or rotating backward during climbing. Using P-Clamps is fine, you must build up a stay bridge using black insulation tape so it doesn't gouge into the carbon material during these forward and backward motion. It's easy to build and any mechanic who has more than 20 to 30 years of experience will know how to do this. OMM recommends the same.