That's similar to the way I did it on the Revell/Monogram 1/48th P51B, and the old 1/32nd scale Revell P51B.
A length of plastic rod was glued into the opening at the leading edge of each flap, assembling the flap halves over the rod. Once set, the hinge access holes were drilled and reamed (later filled with black paint). The assembled flaps were then cemented into the gaps on the trailing edge of the wing, with the inner face of the plastic rod having the adhesive, cemented directly to the inner surface of the wing.
The joint was firm and strong, and didn't require further support.
If you need a sketch showing what I mean, let me know.