Some hardware is very expensive and the site does not earn enough to justify the cost. So necessity is the mother of invention.
PCIe extension cables are widely available. Cutting off the connector and using a wire stripper I have all I need.
I have some 000 gauge wire similar to the kind used by jumper cables which is marked to allow polarity to be respected. I stripped the wire by several inches to allow soldering.
A few plastic cable separators kept the separated wire apart and then I could solder the PCIe cables onto it. I soldered 8 PCIe connectors to the heavy wire. I also soldered one EPS12V connector to the heavy wire. I found some small plastic pieces and they make perfect separators so I glued the connectors into one block to make it more rugged. The spacing was needed to be able to disconnect the cable after testing.
After the soldering cooled I coated the bare wire with some additional thin copper to make sure the entire assembly conductivity was maximized. Adding a bit more solder reinforced the large cable.
After I was done it was ugly but it works. The clamps on the carbon pile easily connect to the 000 cable. Plug in a PSU and see how far I can turn the dial before it blows up or trips the overload. Crude but brutally effective.
The standard test, claim is 650W, tested to 300W before it failed. Clearly the vendors lied about the power rating, I tested my Corsair TX850V2 and it delivered the claimed current easily before it tripped the overload.