Following up on Bizon's script.
You have to add:
[Unit1, Unit2, Unit3, Unit4, Unit5, Unit6] OrderGetIn True
to manually order units to Get In
BUT! They won't Get In without having a vehicle selected for them, using AssignAsCargo like Bizon said.
Unit1, Unit2, Unit3, etc. are all the units in grp, supposing you named the group that.
That is unless the: Load-Get In waypoint method fails.
Beware the GrimMonkey