I have asked this some time ago and was told there is no way but I am trying my luck once more.
Blizzard have lately implemented a "/cast [@cursor] Spell" and "/cast [@player] Spell". However they have not implemented a "/cast [@target] Spell".
If you are a Mage for example you can call out Blizzard in one key press using the macro "/cast [@cursor] Blizzard", assuming you are pointing at somewhere sensible when you press the button. And if you want to play like an Arcane Mage (into the fray), you could also do "/cast [@player] Flamestrike".
But is there a (ingenious) way for an addon to determine the direction / distance of a targeted enemy ? I was thinking if you cast a slow moving spell and check the time taken from successful cast to actual hit, that might give you an indication of distance? I am all out of ideas. And how would direction be relayed in an addon, are there any functions conferring directional information?