@kju-PvPscene
In case this doesn't get implemented, you can use _units joinSilent _group. Though it shouldn't be used on the group leader, because the leader will leave the group and rejoin; one workaround is to temporarily set any unit as the leader (the unit doesn't have to be a member of the squad, so you can create a helper civilian unit for the entire mission), use joinSilent, then select the original leader, i.e:

_leader = leader _group;
_group selectLeader _helperUnit;
_units joinSilent _group;
_group selectLeader _leader;