The next step will be to make the edge connector out of a scrap piece of PCB.

I chose a section with ground plane on at least one side. It was sanded down to fit and scored to make 4 'traces'.

The size of the traces almost matches a PCI connector. You might be able to scavenge a section from an old card. However, the traces leading away from the edge must travel straight together for a while so you have enough room for the cable for connect to them.

I've ordered a prototype connector from BatchPCB and will make it available on their market place once I verify that it works.

Update: You can now get the connector here from BatchPCB. It's $2.50 but there is a $10 per order set up charge from them so you might also want to order the PCB for the switch at the same time.