Bummer but you can't
It seems there is a limit on how many mines you can put on the field. The older ones will disappear. I can't confirm it as I have just tried it one time but that's my first observation.
For maximum fulton mine efficiency, you can do what I add >
If you don't have enough fulton for the heli mission as you can't make it kills its troops, just wait until you have the fulton mine. After the hold up, you can put the mine in the middle of the troops and shoot it with your mk22 from safe distance, you can also do that for the other vehicle types.
The first time instead of shooting it I just walk myself on it to make it explode and I was moving my psp stick as fast as I can so I could flee and not be spotted by the new soldiers :lol Then I gave it some thinking.