Dunno if that's possible. Again, you can open the bays on selecting the bank, and it works for me. You can make a dummy "weapon" with a missile bank that can't actually fire, and use that to toggle between open and closed doors.
Alternatively, FoTG has a script that can control things like S-foils and stuff, perhaps you could use it, and make the doors openable by a special button. Without that, missiles would be locked. I don't think it's possible to make that per-launch. Also, per-launch door opening would be clumsy, as you'd have to wait for the door before the missile flies out. Not a good thing, IMO. When I press the button, I want the missile to launch now.