A light spray of either satin clear, or dulled gloss clear, might work Andy. The problem is getting it to look convincing, rather than contrived or accidental, where viewers may think the finish is incorrect. OK if, when on show, any accompanying descriptive notes explain that the aircraft was waxed and polished, but otherwise possibly open to criticism.
One way you could try, with the current finish, which I've done to achieve a sheen on Luftwaffe aircraft, is to give it a very light buffing, just to create a slight sheen. Again though, an explanation for viewing or competition use would probably be required, to avoid criticism or drop in points.