You may be able to use four bolts, but it will involve some structural work on the wing. It looks like the plywood mounts you have in your fuse could be used for bolts. You'll want to make sure they have tri-stock reinforcement underneath.

On the trailing edge of your wing, the thinner part, a 1/6" plywood plate would probably suffice for reinforcement, but on the thick, leading edge, you would want to be concerned about crushing the wing with the bolts. You would need to do something to strengthen through the thickness of the wing.