The key fobs have a key contained in them. Use those to lock the box, keep the key and hand the fob to the valet and your glove box is locked and cannot be accessed.
I just realized... if you remove the key from the Fob, and give the Fob to the valet, how are they supposed to put a tag on the Fob and not lose it, because the ring is gonna be attached to the key that is now in ur pocket.... there is no ring on Fob once the key is removed.