Don....When I had the Roland G600 I made my own foot sw. controller with a few Roland DP1 foot switches. Wired them to a terminal block and then wired the cable(8 wire cable to an 8 PIN DIN connector)and it worked fine.
All you need is a 6 Pin DIN connector cable (Male to Male). Take the Korg FC5 foot Sw. to an electronic store (Radio Shack may have it)if you can find one pre-made fine! If not and you know how to solder, then buy a few feet of 6 wire coax type cable, two 6 pin DIN connectors and your on your way! Just make sure each wire is connected to its matching connector. For example: when you look at both connectors there is 6 pins staring at you make sure it is wired so the pin in the upper left corner is wired to the pin in the upper left corner of the other connector and so on and so forth. I'm almost certain the 6 pin connectors are industry standard and nothing Korg specific. The reason you need 6 wires for 5 switches is one of the wires serves as a common. Call around your local area first and ask for a 6 wire cable with male to male 6 Pin Din connectors, you might get lucky!!