Boy, that's a *****!
Tell them that you will remove the sensor, it's really easy. (see my post above) Just unscrew the stem and let it drop inside. That way they can't possibly catch it. After they see how small it is, they will more than likely have no issues putting it back. Either way, why not say that you will not hold them responsible if it is wrecked. What have you got to loose? I'll try to scan a pic of the sensor and post it by tomorrow if I can. When they see it, you will not likely get any trouble. Just make sure that you line it up as close to the rim as possible for re-assembly. It has a bend to it which you put closest to the tire. Good Luck!