The Celtics will not have a big FA summer in 2010 either way, but especially not by the method you speak of.
However, there is a viable way for the Celtics to secure a major star who would otherwise be a FA in the summer of 2010. Both Danny and Wyc have touched on this, unsollicited, and it is by a mid-season trade. Even Danny alluded rather bluntly to the possibility of a mid-season trade involving Ray Allen. With his contract combined with other player talent and draft picks, the Celtics CAN get a major 2010 Free Agent. The odds aren't great, but it is possible.