I think the best way to do this would be to treat it as another button in the setup, with its own hotstrings.

For example, if you want your = button to be the + formation.

Hotstrings on ToonA:

= --> FOrA
Q --> FOrB
W --> FOrC
E --> FOrD
S --> FOrE

and so on for each toon, with = going down the list.

Here you come across the problem of not being able to map 2 hotstrings to the same keybind, but since you've got 5 toons and 5 movement keys (=,Q,W,E,S), you can get around that by creatively assigning a different position to each character for each 'main'. (ie ToonA goes left if ToonB is the current main, but right if ToonD is the current main).

You can only set up two formations this way, one with the QWES keys and one with the arrow keys. Can't think of a way to set up more formations atm.