Carpentry and Woodworking - anchoring a double bottom plate to slab

i just had a monolithic slab poured, and fought with my concrete guy about my j-bolt placement. my plans call for a double bottom plate, and the concrete guy sunk the j-bolts in only leaving 2" exposed. what are my options here? i was hoping to leave 4" of bolt sticking out so i could frame the walls on the ground, then drill through both bottom plates before i erect the wall. doesn't the bolt need to go through both bottom plates?

Try a barrel nut and a short piece of all-thread to extend the anchor. The hole will need to be larger, which will require some large washers.

Perhaps have a short piece of threaded rod welded to the anchor.

If it were my project, I would use a hole saw to cut a hole in the top half and then use a regular nut and washer on the bottom portion.

You might rethink the need for a double bottom plate. I would use a PT sill plate bolted on with the J bolts. Frame your stud walls on the ground with a single sole plate. You'll have to bore the bottom plate to accept the sill bolts/nuts.

You may be able to find coupling nuts and extension rods