I guess this is not possible, otherwise it would probably already have been done, but could there be a mod that automatically adds this feature (adaptive) spots to a map, even when the map has not been designed with this functionality in mind?
This mod would need to execute a script at start-up of the game, and the script could for example do the following:
Iterate over all metal spots on the map.
Check whether the spot is within some range of an army spawn point.
Check whether that army has spawned for the game.
If not, then disable that spot.