A Carradice saddlebag may sound old-fashioned , esp when combined with a high-tech carbon frame but its makes alot of sense. You can get support racks with quick-release mountings that attach to the saddle and there is less metalwork than traditional panniers or racktop bags. The bags come in several sizes up to the size of a large daysac. They weight little, can take a lot of weight and aerodynamically they have the advantage over panniers or racktop bags.

Carbon fibre is strong when used correctly but you shouldnt crush the tubes with P clamps. If you really, really want to mount a pannier rack you could dremel some suitable material (Al or carbon fibre bar) into a mount, with suitable load-spreading shape and epoxy it to the seatstay...at your own risk.