my guess would be that he runs his 3 or 4 characters in a quad screen fashion... hits the key for blizzard... at which point all mages are waiting for a target... then he just goes to each quadrant (maximizer would look like a 2x2 grid of screens) move the screen to point to the target if needed, right click to cast, then move to the next screen. if they are all looking in the same direction, just slightly off, then you would only need to right click in each of the 4 windows to cast.

it wouldn't be exactly simultaneous... but it'd be good enough.

nice job

(let me know if you need some info on keyclone's maximizer)