I've never made a KCY extension, but I'm with Robb on this. IMO.... if wiring up the collettes was fairly simple, I think that more folks around here would be doin it. I think that is why Nick's knowledge is priceless. He wires the collettes, correct? I know that you can purchase the collettes with cable attached, but I "think" that Nick does the work..... maybe??
Just a thought out loud..... maybe a pair of "wired" collettes could be ordered, and then "spliced" together via a junction box??
Delicate work with expensive parts + Not much knowledge with the parts = A potentially scary lesson learned.