My improved Tesch-Rack. Not really lightweight... I am planning to mount the panniers as near to the driver's seat as possible and wanted to be able to move the panniers backwards. Now I have three possible ways to mount the panniers.
The original Tesch-mount has been replaced by some laser-cut sheet. The keyhole-shape holes are designed to take screwheads. Note the tiny catches for the fastenings on the vertical bars of the extension - three of them for the three possible mountings of the panniers. Story: The middle position (leading to two smaller extension on front and rear end) would be the way you mounted your panniers. (The bending of the sheet results from the camera's lense)
The way the panniers are finally fastened after putting the screws (to be drilled into the tire-faced side of the panniers) into the keyholes...
... on both, front and rear side. - As you can see, just one extension would do. I am thinking of mounting a tripod on the top of the rear extension (or even having removed the rear extensions, for they are quite heavy).