I've just followed the instructions to fit a redarc unit tonight. Redarc do a cable for their controller as well as the Tekonsha one mentioned but you still have to swap the wires around (sigh).
Attachment 187479
I decided the best way to fit the control knob was a bent piece of aluminium strap nicely polished and mounted against the centre console. No holes to drill and can be removed if I ever feel like it, the control unit was mounted in a similar position to where others have done it.
Attachment 187480
Sorry about the out of focus picture but you get the idea....
Regards,
Tote