Three
Tour Rookie
The rules do not have anything to say about club selection, whether you play with some left handed and some right handed clubs, whether you play a shot opposite handed with the back of a club or by turning the club round to play with its face etc. Your player who carried a mixture of right and left handed clubs is not obliged by the rules to use any particular one at any particular time. He has complete freedom of choice for any shot including the one near the staked tree whatever he said to you. If the club he selected for that shot resulted in his gaining relief from the staked tree, that's just a consequence of his freedom of choice.
Have you forgotten my very first question on this forum, regarding my pp who deliberately chose to play a wedge from 300 yards away in order to get a drop when in reality he wanted to play a 3 wood? He took the drop because his wedge stance was affected, then swiftly pulled out his 3 wood as planned.
The R&A advised that he did not have the choice to choose any club or shot he wanted simply to get a drop.
I see this as an identical situation. 100 times out of 100, the guy would have played left handed from the given distance. All of a sudden, however, he deliberately tried to claim that he would play right handed, this was done ONLY to get a drop from an iffy lie. Exactly the same decision should be applied imo, no relief, as there is no interference from the shot he would normally take if the obstruction wasn't there.