Two options really. Either:
* When sorted, kick the helo pilot out of the group:
(driver helo) join grpNull
You'd then also have to give the pilot more movement orders, without being able to set them in the editor (since the pilot starts in the player's group). Probably not a good plan overall and plenty of ways to go messy.
* Rather than starting with all players and the pilot in the same group, have them in different groups, but then you'll need to move the soldiers into the helo manually, rather than just by setting "In Cargo" in the drop-down list, since they are no longer grouped with the helo:
this moveInCargo helo
helo waypoints 1) "Transport Unload" where you want dropoff 2) "Move" back to base or whatever.
soldier waypoints 1) "Move" to where they want to go after dropoff - synchonise this waypoint with the 1st helo one.