Why not play the scenario twice with sides flipped? Scores would be combined from both games to be treated as one match. Squadrons would be allowed to have different members in each game, too, so that they could field their two-seater expert in one game and the Nieuport 17 experts in the other

Scoring kills might not be so good -- the winning strategy is to get the first kill then exit all your planes off the map!

Maybe just score the total points of both matches.

Or maybe have the number of 'goals' be the number of your side's planes left on-screen when the match is over. And have all matches end at turn 30 if they're not over by then.