What you might possibly do is to use this tool for trainingmissions.
You can create different scenarios in certain training-facilities where you have for each mission different tasks to do. Starting, landing, landing on an open field, flying to certain spots and return, simulated bombing runs etc.. One can create maybe 30 such missions and save it as scenario missions, doing one mission after another and then joining your squad after completing all of them.
While doing trainingsmissions one could add different friendly flights with different AC etc., simulating other pupils doing their trainingjobs while you are doing yours, so the trainingfield looks and feels crowded. Or depending on era you can use different AC while learning to fly.
The only thing one would have do is having the "logs on" for all flights, not only campaign, and after each mission going into campaign and skip one day forward. That way your squad is developing as well while your are doing your training. After training is done (with all various missions and tasks in scenario) one joins the squadron and starts his actual campaign.