What's wrong with just having all your characters in the team list?

There is always the possibility to make an ISBoxer enhanced wow macro similar to the /invite team in game helpers. Maybe you have to run it on all chars.
/ema-team removeall
/ema-team add {SLOT1}
/ema-team add {SLOT2}
/ema-team add {SLOT3}
/ema-team add {SLOT4}
/ema-team add {SLOT5}