1. Enter the vehicles (this breaks focus).
2. Set the leader as focus, via /Focus NameOfToon.
3. /Follow Focus
4. /Assist Focus (or /Target FocusTarget)


Khatovar posted this macro, a ways back:

/assist Focus
/click [target=vehicle,exists] VehicleMenuBarActionButton1
/click [target=vehcile,exists] VehicleMenuBarActionButton2