Pickoff to 1st - contact with rubber

[Zapruder]

Hi
Apologies if this has already been asked and answered - I searched the forum and couldn't find anything completely definitive.

We're having a little debate at my club in South Africa about whether a pitcher is allowed to stay in contact with the pitching rubber when picking off to first or whether he has to remove his pivot foot first (e.g. either by stepping back off or doing a jump turn).

The MLB rule seems to imply that he can pick off to first with foot still in contact with rubber, because it says that if he feints to first while in contact with the rubber and doesn't complete the throw it is a balk. This implies that it is legal to pick off to first with your back foot in contact with the rubber (as long as you step towards the base).

Rule 8.05
(b) The pitcher, while touching his plate, feints a throw to first base and fails to complete the throw;

So my question is - can a pitcher legally come to set position then turn, step towards first and throw, while his foot is still in contact with the rubber?

Thanks!