Or you could just set a focus and make all your macros assist this focus?
http://www.dual-boxing.com/wiki/inde..._set#Set_focus
/assist [target=focus, exists]
/cast (spell)
This will assist your focus and will then cast. When you don't have a focus set, the character will act like it is played solo.
You could make the same macro differently:

/cast [target=focustarget,harm,exists][exists,harm] (spell)
This will fire at the focustarget(if it exists and is harmful) and otherwise will cast at your current target(if it exists and is harmful)