My atb commuter has no rear dropout eyelets for a rack, of course, and I am wondering if there is any kind of system that can hack maybe forty pounds. The closest I've found is the Topeak MTX Beam:

TopeakŪ Cycling Accessories ? Products - MTX BeamRack (V-Type)

...which can take twenty pounds of cargo.
I've looked with some curiosity at my unused disc brake mount holes on my left rear dropout. I suppose it is wild and unreasonable to think about finding and somehow mounting an identical hole-mount on the right side dropout and use them for rack "eyelets", but I guess I just like projects.
It seems I might be restricted to a seat-tube mounting system, but I see no real reason why a system that makes use of the rear stays or dropouts as support structures could not be devised.