2 of the corsair AX1200i model modular power supply units.

I hook thr 24 pin cable that goes to the mother board to the 2 PSU (Powers Supply Units) with a PSU2 cable splitter it joins 2 wires of the 2 psu to  make them both realise they are switched on from the mother board.

They sit separately ( individually) in the same rig tie wrapped to the frame, and just joined by 2 wires out of the 24 pin cable block that goes to the mother board. You can buy them at most places ebay, amazon or pc suppliers for around £10.

1 powers 4 cards, the other powers 2 cards and the mother board.

You can just do it with a pin or paperclip if you really want to. just join the green and the black on the psu not connected to the motherboard

Tope that info helps.