1h left swing, polearm right swing, and both 2h sideswing directions can pull off this "hiltslash". Keep your opponent just off the shoulder you are swinging from, look up or down slightly (not necessary with the polearm animation), and turn rapidly into your swing. You can do full damage very early in the swing animation.
For the record, I think hiltslash is dumb, for the sole reason that it makes fights look like a ridiculous squaredance instead of an epic swordfight. I don't think medieval knights were spinning around trying to keep their enemies on their hip.