The Celtics have about $48.5m on the payroll for next season, including Joel Anthony's option and excluding the unguaranteed contracts of Phil Pressey and Keith Bogans.
If we use the estimate that the cap will be at around $62 million, that the Celtics will have a cap hold of around $5 million for first round picks, and that Carmelo Anthony is willing to sign a contract beginning at $22 million, the Celtics need to cut $13.5m in salary.
If the Celtics renounced all free agents, doing a salary dump of Joel Anthony, Brandon Bass, and Vitor Faverani in a trade where the team sends out draft picks and takes no salary back would only get the Celtics to $12.7m. If you could get Melo to take a bigger pay cut, then that means you wouldn't have to trade Green or Wallace. Otherwise, you would have to move Green or Wallace (and have the ability to keep one or more of those players, or if you move Green or Wallace in addition to three previously named, you could re-sign Bradley instead of renouncing him) or move Olynyk if you think he is worth less than the draft picks you might have to give another team to take on one of those contracts.
So, it is theoretically possible for the Celtics to put Rondo, Wallace, Green, Carmelo Anthony, and Sullinger on the floor together. How would you like that?