Theoretically, it MAY have been possible at the start of the 09 offseason IF:
1) We let Rajon Rondo and Ray Allen go at the end of the 09-10 season;
2) Paul Pierce opted out of his 2010-11 contract to leave or to accept a lower salary in an extension; and
3) We didn't add any more players this offseason to more than one year contracts.
However, that has been negated by two things:
1) Signing Rasheed Wallace to a 3 year contract and
2) The fact that the salary cap decreased this year and the forecast that the salary cap will decrease more significantly next year.
We cannot "add" a max player next summer by free agency; we can only sign a max free agent if he already wears green (i.e., Rajon Rondo gets max dollars next year).