If you have some free space between the gantry uprights travel path and the table, you could use some wooden blocks on the table frame (just to the right of the T-slot).
Make some T shaped blocks that can be extended past the T-slot such that the long part is away from the table and the bolt for the clamp passes through it and into the T-slot (supporting the back-end of the clamp on the protruding end).
A fixed pair of bolts in the T-slots (one either side) and a bridge piece between them with the material between the table and bridge.