Is this pick-off legal?

[Larry1953]

OK, can any fielder without the ball straddle his base? Of course he can. With a runner on base, can a pitcher straddle the rubber without the ball. Nope, the rulebook says that is a balk. But I thought you said when the pitcher is not in contact with the rubber, he can act like any other fielder? In this case he can't.

That brings me to a question about the hidden ball trick. The rules say a pitcher cannot straddle the rubber without the ball... Presumably this disallows undue deception while trying to pull off the HBT. What I am unclear on is whether the pitcher is allowed to go up on the circular lump of dirt called the mound without the ball in his possession when play is "relaxed" or is he just not allowed to stand on or straddle the rubber?