For almost every vehicle in the current game, the FTL Follow Me (mapped key) causes the slaves to follow.
If you press "1" (or any other key) while in a vehicle, the others assist correctly and press the same ability number.

You don't need any special macros for follow or assisting with IS Boxer.

When I choose to exit the vehicles, I just press (G2) which is my hotkey to turn Mouse Repeater on.
Move my mouse on the main screen, to the exit vehicle button, click it. Then press G2 again, to turn Repeater off.



*Edit*
The only vehicles which have been a problem so far, are the Dragons you ride, from the Temple in Dragonblight for the daily quest.
For some reason, could not get those to follow, using the default (no special macros) IS Boxer controls.