I agree that he'd be good to get but not realistic. In order to have a chance, Chicago would need to want to use a few of their pieces to upgrade at 1 position, and we'd have to be willing to deal Ray, basically. In that case, we'd need to take back some combination of Thomas with Hinrich, Hughes, Safalosha, Nocioni, Deng, etc. I don't think Chicago would be willing to deal a package for Ray that would make it worthwhile for the Celtics.
For example Ray, Baby, Scal for Deng, Hughes, Thomas, Safalosha works cap wise, but would either team want that?