The only way I've found so far is to use:
/bind KEY "targetcustomnext notmypet"
However, that will toggle through everything...friends, enemies, pets, glowies, hostages...everything, except your pets. There may be a better way to target just glowies and hostges, but I haven't found one yet. Maybe someone has found something better and will post it.
But as with anything, there has to be line of sight to target them. Nothing would allow you to target them from say another room or the other side of a wall.
If you get lucky and the person you have to lead out is the kind who fights beside you, then the commands to target_friend_next and such will work as they'll be considered an Ally by the game.
is there a way to target hostages, creatures, scientists, etc.. that you have to rescue/lead out? Sometimes the last few are hard to find in those big outdoor missions.