This map demonstrates how you can lock a structure's "bone_turret" bone to a unit just like you can "bone_chest" and "bone_head" more details in the map. Perhaps UMSWE or some other WE would be interested in this?
the only two that came to mind :P though I think the other ancients do too plus any of the special towers in the Blood Elf bonus level. I think there are probably more I just don't know which ones have turrets you'll have to experiment ;)
there's a trigger, Animation - reset unit bodypart facing, I didn't use it in that map though as it was just to show that turrets could be locked by triggers too.
Ah I didn't realise you had meant JASS :P and it looks cool, will try it later. I was thinking of trying something like this but you beat me too it, glad to see my discovery put to good use :)