Nat's cable swap is the way to go.
A standard Duo controller cable gives you about 4' 3"
If you can find one, the aftermarket cable from a TZD "Duo Controller Kit" is a nice 5' 5"
Cannibalize a broken Turbostick and you've got a whopping 7'
The sacrificed controller can still be used by taking the leftover stump cable from the Tap, reversing the wiring procedure, connecting it to controller, and then always using it with a cheap extension cable.
The problems experienced running a Tap through an extension cable are quite strange. I played halfway through Double Dragon 2 with a friend once without problem and suddenly we started fighting for control of each others' characters. Other times problems are immediately apparent. I have two different beige, Duo extension cords and one official TG16 cord and haven't had better luck with any of them. I've also had six-button controllers malfunction when used with extensions.