doing this from aphone- wont be home for a couple of weeks
basically adding a custom aerodrome without a runway 'fools' the game into performing a squad scramble. this is the only way ive worked out how to do this- and it can lead to hillarious results
planes pilling into hangars etc etc. careful choice and positioning of the custom aerodrome and choice of wind direction-planes always take off into wind.
i used 2 added aerodromes, 1 for each of the 2groups of planes. trying to add 2 groups to 1 airfield usually results in planes spawning on top of each other- ie a big bang and a hole in the ground
have fun experimenting