Started with ordering 5 decently shielded 1.2m cables from Digikey. (the longest they had in decent shielding) The cables use RG142 that has two shield layers and gives about 90dB shielding. Unfortunately it also costs double everything else :-(
Will try your trick of separating out the attenuators with the decent cable in between.
Also will try seeing if I can set-up a shielded box for the receiver. This may be especially tricky as RF seems to leak in/out everywhere and I don't yet have the budget on the project for >$10k equipment acquisitions. It will most likely have to be a jury rigged device made from coffee tins with tin foil seals and a few soldered earth straps.
That means I am still be very interested in what you find because I don't have the greatest faith in my jury rigged capabilities. Its also going to be a week until I get may hands on the cables as I missed the direct Saturday flight out Memphis.