gaijin san
Super Freak
The bomber jacket and helmet should easily go over the USO suit.
It's not as simple as that, you've got at least one more HS, two if you want an unmasked portrait, different gloves, belts and bandolier, combat trousers, then knee length gaiters/chaps then new boots. I wouldn't want to be putting those gaiters on and off over the USO uniform. In fact the only pieces this would have in common as a figure would be the USO top and the shield. Makes sense that it'd be two different figures. Plus, as Howard says, likely to be greater demand for the WWII outfit.
And yes HT are in this to make money, that's how companies survive. I don't think making separate USO/rescue mission Cap's is an unreasonable move.