The difference with Ray and with McHale and Havlicek is that Kevin and Hondo were largely 6th men early in their careers and later became starters. It's harder when it's the other way around. And remember how Ray got rattled when all the trade rumors were floating around 2 years ago. If anyone shouldn't have his routine changed, it's Ray.
Red Auerbach did once say it doesn't matter who starts a game, it matters who finishes it. However, I'd also add, though, if your goals are to rest Ray more, bringing him off the bench doesn't do anything. If Ray needs to play fewer minutes, he can do that as a starter just as easily as a bench player.
I think the real issue is going to be rotations. Doc's biggest problem is mass substitutions where he waits too long to rest any of his starters and is stuck bringing in an entire second team or overplaying a tired starter. If he instead took Ray out 6 minutes into the 1st quarter, he could get him some early rest and have someone to play early in the 2nd quarter.