I take a piece of material such as c/a hinge material and cut a hole in it slightly smaller than the bolt . Then I apply ca to it and let it dry, then put the bolt thru the wing and screw it thru the material. Most of the time there is enough space between the wing and the block in the fuselage for this to fit. The material fits the bolt tight enough that it will not just fall off but will retain the bolt.
Fred B