I tried a few tricks found via Google to ‘unlock’ the menu, but with no luck.
I purchased an inexpensive universal remote to try to change the input mode; this was disabled.
I learned of the green Philips Master Remote RC2573GR that has a ‘master’ and a ‘guest’ mode to change TV settings- but these run $35 on eBay.
I found one post that suggests the Harmony does have codes for the ‘master remote’. I picked up a Harmony 200 remote for $20 from Radio Shack and I will try this when my clothes are done at the laundromat.
Just to be safe, I also purchased a RadioShack 15-2526 RF modulator that will take the composite video and audio from the Gamecube and inject the signal over channel 3 or 4 ($30). If the Harmony does the trick I can return this…
Update: The RF modulator worked, but it is very cumbersome to use as I must also keep a set of needle-nosed pliers to remove the coax cable from the back of the TV. I purchased a generic Philips master remote for $33 and it allows me to re-enable the external ports. Once enabled, there is a new option on the menu from the standard hotel remote to change inputs- and this option appears to stay once renabled (at least for a few week).