8.05 (d)
If there is a runner, or runners, it is a balk when—
The pitcher, while touching his plate, throws, or feints a throw to an unoccupied base, except for the purpose of making a play;
To me this would allow for the throw to second, but it also seems in conflict with 8.05(a), unless a "pick-off play" and "making a play" would be considered the same. I too had always thought that it was illegal for a pitcher to throw to an unoccupied base without legally disengaging, but once I began umping and getting into the rules I now know better. I've never seen it done, but would love to witness it on the major league level.