As the bottom connector of the Transformer is the charge port, it would make sense to have two such charge cables connected at the USB 3.0 ends with a dual female connectors then the males ends would act like a tether cable that effectively connects the Transformer to the keyboard dock. A low tech umbilical cord!
It would only need that (mod) tether cable, and perhaps the connector switch on the dock (half)closed to signify a connection is made.
Think of the possibilities, I would just scrap the actual cable and go with a dongle and make it wireless via wifi, BT, IR, ...
Now that would be a mod!!!!!!