Pix in Miscellaneous:2010:Series C. The rack is fully sprung and the seat half-sprung. You can see where the fixings are, one on each footrest plate, one at the saddle nose. The ally plates are structurally redundant, and could be dispensed with, but doing it that way meant that the rack didn't have to be welded to two decimal places to take the pannier "pegs and sockets". You can see the pegs at the top, and the Dzus fastener at the bottom of the plates.
If the fixings for the plates were approximately correct, I could fix the panniers accurately to the plates, then the plates accurately to the rack. I didn't want to fit a tail rack, or a hideous top-box (ALL top boxes are hideous), which made things simpler. The "lifting handle" at the back needs to be higher to let the mudguard flap lift up further, but it isn't a show-stopper. I've made many trips over four years, fully laden, had no problems, and it makes no difference to the handling, possibly because it isn't cantilevered out far astern. A side benefit of the plates is that they keep muck off the panniers themselves, so I don't have to hose them down on arrival to keep tents or hotel rooms clean.
The whole shebang is readily removed, but in fact I've never removed it. I occasionally leave the panniers behind which is how I know there's no difference laden or unladen, except that the suspension bottoms more easily laden. As it would do.
Do you have a sprung saddle? I would be interested in the design if it is articulated for the standard setup. Either way, actually I would be interested. Maybe post them in the Photos section?