I think that would be the only way, unless you made a unit that could not move, but maybe could paradrop (or equivalent) to its placement, and was, like the aircraft carrier, active defense when it has activator on board.
You can use SLIC to disable the (Victory)Movement of a unit. This way you can create a unit that can't move and can attack but it will remain in place if it wins a battle. Is this what you mean? Again using SLIC you could automatically create one of these units on every tile with a Fortification tile improvement on it.