I'm not sure if this is what Zakk up there's spell does, but you could try using flying heights, decreasing the dummy unit (the hammer)'s height progressively so that it looks like it's falling from the sky.
That model looks good, and you could also experiment with the gryphon hammers or the storm bolt, changing the scale and the pitch angle (or something like that) so that it looks like it's been dropped directly from above.