It would be very easy to do this to the AT-AT with the right hardware from the good people at Krauss-Maffei Wegmann:
And more to the point, why were Snowspeeders specially equipped with "harpoon guns" in the first place?
They came in handy against the AT-ATs, but what was their normal function supposed to be?
Whaling operations on Hoth between combat sorties?