[Tom Line]

However, the "rumble" is a small motor inside the gamepad.

Would you violate the motor rule? I can't recall, but I doubt it.

Anyway, if you checked the motor specs you could probably just cut the power leads from the motor and use the digital outputs on the DS to run them if the amperage / voltage line up reasonable well. Then you could just turn it on/off to turn the rumble motor on/off.