I would assume it can be done with a simple 3 way switch, attaching the bidirectional data line that goes to the console board in the middle lead, with the Bidirectional data lines connected to the internal and external controller ports each on, an outside lead. I may be wrong but I think that's all that's needed, as you can leave the 5v, and 3.3v (and ground of course) connected to both the internal and external controller without a problem. If I am wrong, will someone more knowledgable correct me, please?
'''''''___
'__|''''''|- to internal controller data line
|__|''''''|- to data controller port on board
'''''''|__|- to data line in external controller port
Ignore the apostrophes, I used them for spacing.