Can't you use:

/cast [target=party1target] spell ?



I only dual box but with my priest I can use a macro like this:

/cast [target=party1target, harm] smite; renew


So to dps I just target the enemy with my pally and use this macro, to heal I just target the friendly target. Saves me space and is very simple to swap from dpsing to healing. (I'm at work so the macros might be a little off since I don't have them in front of me 8| )