How I do it.

Picture sequence is bottom pic., top pic., 3rd one down, then down in order. I even got two the same.
.First get a drinking straw from McDonalds. It's larger in diameter than most others and slips over the clevis and ball link easily. I don't know what order the pictures will be in but there messed up now. The first pic. should be of the bellcrank to flap pushrod made from 4-40 threaded rod screwed into  the ball link and the metal clevis is attached to the other end. The next pic should be of the inside of the wing as the straw slides up to the ball link in preparation to slide over the ball link stub end. Then push the straw into the wing forcing the bellcrank to turn as far in as it will go. Next pic. shows the outside end of the straw with a mark at the pushrod cutout end so the straw will catch on the opening holding the bellcrank in the far in position jamming the bellcrank in position. Next pic should be of the cut off straw stuck in the pushrod opening. At this point you would be ready to install the wing for the final time. You would unscrew the pushrod from the ball link counting the turns so you can get it installed exactly as it was. Slide the wing through the opening in the fuselage being carefull not to poke the straw inside the wing. Once the wing is in position you are ready to re install the pushrod. The end that screws into the ball link should have a taper ground into it so it will find the threaded hole easier. Be carefull not to release the straw until the push rod is caught on the threads of the ball link. Turn the push rod in the same amount of turns as it came out and your done. I mark a stripe in the push rod and double nut the end and use a nut driver to install the push rod. The pic. of the long straw with the cut off mark has the number 19 at the bottom on the trailing edge of the wing, that's the number of turns of the push rod during installation. The thread pitch is .025 per turn so that is .475 of thread engagement.
  Doing it this way allows you to install the wing without cutting the doublers and weakening the fuselage. I've had a couple planes crack when I cut the bottom out and even glued in reinforcement. This works on profile planes with the reversed bellcrank.