[Mobhack]

Then use the cross-attach command in the deployment screen. (You cannot cross attach away the formation leader though). Mouse over the buttons till you find the guy "saluting" and the info text is "assign current unit to a new HQ". Click the unit you wish to assign, then click on one of the units in the desired formation.

If the cross attaching puts the leader away from the 0 unit, then use the fix formation leader button in the formations screen (only if you have the full game).

cheers
Andy