Hi, it's possible but not in macro, but with an addon.
Try this addon : MySpecialTargeting :
https://mega.co.nz/#!oJZWwCIC!8RMI1gYflRBw_xWFQly_xzVF3-CTUFyyCgJ-fYroyhMFor use this addon you must to do this macro : /run MySpecialTargeting("Holy Shock")
Info : mouseover = all unit (player, npc, ennemy ...) except you.
What behavior do you want when you use your macro bind without shift held, without target and without player under your mouse, your cursor will be like that :
Do you want highlight or not ? (highlighted cursor = ready to cast on next unit clicked except you)