So it turns out that you don’t need the table to clip through the ground. You can instead clip through the ground via a conveniently placed hopper (which you can see in action in the link below). It will only work when the bottom of it is facing the wall.
http://www.sendspace.com/file/buieds
PS. If you take out the turret at the beginning fast enough (it only works with an SMG grenade or a rocket), Barney will immediately say “Great, I’ll open this up”. You can see that done with an SMG grenade with this link:
http://www.sendspace.com/file/qbnssg
(Performed on Source Unpack)