+1 for mousetraps. You should be able to easily build it into the table top and the actor sitting behind the table could trigger it quite easily. The beauty of a mousetrap is they're designed to swing a full 180 degrees, so the wire will spring up, shatter the glass and keep on going to become hidden in the table again. A simple slit in the tablecloth should help to hide the gimmick if you've got a balcony.
One thing to keep in mind though is that some mousetraps fire with a fair bit of force. You might need to experiment a bit to get one that doesn't end up spraying sugar glass everywhere or knocking the glass sideways, which would ruin the effect. Securing the stem of the glass to the table could help mitigate the second of these possibilities.