I think it's a good idea, even if KG doesn't agree to sit. Choosing to rest Pierce or KG into strategic games (during a series of back to back or on a road trip, for example) would be great for the playoffs, and we certainly have the ability to win the games without one of them.
I know Phoenix is bad, but Green can perform well enough during KG or Pierce's absence to lead us to a win (along with his teammates' contributions of course).