If I have 5 characters I want to split into a star formation I cannot do this with an arbitrary leader. However if I can press 2 keys at once depending on who sends it I could...

However it would require a fundamental change in the way hotstrings work. Each hotstring would need a direction associated with it and each client would need a send and recieve for each string it wanted to handle.
My leaderless, focusless hotstring setup can easily form line-behind formations based on an arbitrary leader using hotstrings (Driving on Toon A, B stands still, Toon C moves left and Toon D moves right. Driving on Toon B, C stands still, Toon D moves left and Toon A moves right and so on) I can see no reason why mapping a second key in a similar way wouldn't do exactly what you desire. I've not tried to set up a star formation (I only quad) so I'm not sure on the directions you want the other toons to move.

Code:
ToonA:
F --> FormationALeader
LEFT --> FormationCLeader
RIGHT--> FormationBLeader

ToonB:
F --> FormationBLeader
LEFT --> FormationDLeader
RIGHT -->FormationCLeader

ToonC:
F --> FormationCLeader
LEFT --> FormationALeader
RIGHT-->FormationDLeader

ToonD:
F --> FormationDLeader
LEFT --> FormationBLeader
RIGHT --> FormationALeader