YOu mean to cast Arcane Intellect for example right?
I would just put the spell on the same number area for each toon.
Ex. put AI on the 7 key for all toons. Then I hit esc so they dont target anything, then hit 7. (make sure you have self casting on) and they all buff eachother.
If you have different classes to cast on, then you would have to make a slight change, put the buffs to 7 AI, MOTW, PWF, then hit your F1-F5 buttons and hit 7 after.

You could set up casting sequences for it, but it would be much more work to make the buff then to just do what i mentioned above.