The rules don't allow for any kind of wireless transmitter on the minibot. You can use an NXT module on the minibot, but the wireless Bluetooth functions have to be disabled.
We are likely going to use a limit switch that came in the KOP. Limit switches are in the allowed list of minibot parts too.
Some limit switches look similar to this:
When the lever on the side of the switch is held down, the circuit will be open. When the minibot is deployed, some mechanism on the host robot should release the lever, which completes the circuit and activates the minibot.