You can lift the carpet out quite easily.
Find the screw thread.
Then cut a flap in the carpet with a sharp Stanley knife (cut only 3 sides a the square).
Fold this flap back to use the bolt.
When you want to return the car to normal the flap will sit back flat and nicely into the hole where you originally cut the carpet and will not show.
You could tape the underside of the flap when you have finished with the bolt hole if you wished.