A wire hanger with a very short 90° hook bent on one end works well for fishing an end cap out of the wing tube. Try to snag one of the rivet holes in the end cap.
Why do you feel the need to strengthen the wing pipes? They're plenty strong on their own, unless you've welded them (destroys the heat treatment). Making them stronger makes the wing tube in the hull the weak point. It's much easier to fix a broken wing (replace) than a broken wing tube. Also, the end of the pipe inside the wing tube creates a hard point (break on the dotted line), unless you create "fingers" on the end of the pipe to spread out the transition.
Positive flotation? The wings should never be on their own in the water. Shooting foam in them just adds weight and a potential source of trapped water = corrosion. Bad idea.
I'll try the coat hanger but the cap is jammed in so I may need and alternate if that doesn't work.
Boat is a 1986, wings have not been welded but I notices some corrosion inside the wing "pipes" (actually found one pinhole) so I plan to proceed with inserting the aliminum pipe. Good idea about making fingers for the transition - Thanks.
Foam trapping water in the wing makes sense, so I'll pass on doing that