It's funny, because I actually made the USA 5120x3276 map exactly for this. Actually, besides editing the size of the station coverage, you can 'cheat' by extending your airport's coverage by putting Parking 'stations' (this is under the road menu. storage size 64).
The one airport 'station' covers both cities
In this screenshot I was lazy so i didn't remove any parking, but as long as they all share same station, once they are extended out you can remove parkings here and there while maintainging same station coverage.
This is the main hub for my company

This is my route map.
