1. Load into Game Master.
2. Create US playable faction (for this example, should work with any faction).
3. Place US spawn point.
4. Pace Random US Soldier (though it works with any allied soldier) near spawn point.
5. Use respawn menu to spawn on spawn point as a player and leader of a group.
6. Move to the previously placed US soldier and recruit them into your group.
7. Switch back to Game Master.
8. Place Random Civilian (though it works with any character) nearby.
9. Take control of civilian.
10. Stand near AI-controlled US soldier and give a move order (using the radial menu) to a point in the distance.

At this point, the AI-controlled US soldier will follow the orders of the Game Master-controlled civilian, as if they were the group leader.

This seems to work with all orders, and works when giving orders from an enemy faction (Soviet soldier commanding US soldiers). There may be other unexpected interactions related to commanding in Game Master, but I did not test other possibilities as thoroughly (for now).