I would build it per plan up to where you want the section to end, then take that rib and make two out of plywood, use a tube and sleeve that fits that rib and a dowel pin at the rear to align them, and finish building the wing per plan so the length remains the same. Do the same for the other wing, then instead of following plan for the center where the wings would normally join, make a spar section that joins the two panels at least two ribs out on both and epoxy the center together. As for joining the outer panels, you will need to come up with that on your own since I don't have plans that show the wing. What I have done in the past is to use a 3/16 - 1/4" plywood plate that is epoxied on either the wing panel, or center section that slides into the wing and secure it with a T-nut and bolt or two.
On my B-25 I have a setup like this, the aluminum tube is glued into the outer panel, the plywood plate is under it on the outer panel, and the T-nuts are in a plate above the tube so the bolts go in from the bottom, through hardwood blocks under the tube in the CS, through the tube and into the T-nuts. Secures the wing tightly and only shows the small holes underneath where the bolts go in, the heads flush with the surface.
