Try:
/castsequence reset=120 War Stomp,,,,
etc.

If you hit the button within 2 minutes of the last time you hit the button, it will just move to the next toon and cast it for them (since their macro will be at the same position). If you don't hit the button for 2 minutes, it will set back to being toon1's turn. The result being that toon5 will rarely ever cast it. I use this with Frost Nova, and it works great.