Thought I would throw this idea out there...
Could we have the option to add a helicopter expansion to an ambulance station?
The helicopters in my area are based at an ambulance station, hence my suggestion. I'm guessing there are other setups across the world which are similar 
Perhaps adding a 'ground vehicle/ambulance' expansion to a helicopter station is already possible? I'm presuming the answer is no, but cannot confirm either way.
At the end of the day, it's not a big deal if we have to build them separately. Just thought I would see what others think? 