I think it's time for D'Antoni to say to Amare: "We're not going to give you help when you're defending guys in the post. We're not going to double down to help you out anymore."
Amare had reason to struggle against opposing centers, because he's not really as big as many of the players that he used to have to guard. Now, he's playing at power forward, and there's no reason that he shouldn't be able to contain anyone at that position. If D'Antoni says, straight up, that he's not going to get help, there will be no one to blame when a pf goes off besides Amare. Double-teaming is kind of a defeatist strategy, anyway. It is like admitting that you can't guard a guy straight up, so you try to finagle a scrambling type of defense to make up for one's size shortcomings. Amare is a prideful guy. I doubt he'll appreciate getting embarrassed in the post if he won't be able to say, "but wait! The double team was late!"
The way Nash is playing lately, I think Amare is now the best player on this team. That's not exactly a great thing for the Suns, because in the past, Nash's ability to dominate the game whenever the team was challenged - be it in the fourth quarter, or when the opposition made a run, or anything like that - was so often the difference between winning and losing. If Amare wants to win a championship, he has to start making the plays that nobody else on the team can make. And that starts on the defensive end. Instead of D'Antoni figuring out gimmicky ways to hide Amare's deficiencies, Amare needs to find out ways to stand on his own and help the other guys on this team that can't do it themselves.