Macro assistance, blizzard

I don’t think this is possible but thought I’d ask. I want to build a dungeon macro that targets the tank, or the tank’s target (so far no problem) then casts Blizzard at the target (problem?), then targets the tank’s target for the next cast (again, no problem).

Th difficulty is the blizzard cast as, if I understand correctly, it can only be done by tooltip. If true I’m kinda screwed on that part.