Rule 8.05(a) Comment: If a lefthanded or righthanded pitcher swings his free foot past the back edge of the pitcher’s rubber, he is required to pitch to the batter except to throw to second base on a pick-off play.
This say's no.
So on Dash's field, cool (if the runner is going).
On my field balk.
This is why Lefties do not break the plane with R1, cause if they do, guess what they gotta deliver the pitch no matter what R1 does, I call it the same for a righty.