I am pessimistic about some team trading for Humphries to bolster their bench near the trade deadline.
For one, his salary is just too large to be easily moved at the deadline to a playoff team that is likely to be over the cap and without good options for matching salary.
The other team almost has to be sending out a big salary (I'd say big enough so that the other team is allowed to send that player plus a minimum salary guy and take Humphries back) and I just don't see likely candidates for that purpose on possible contending teams. It'd probably take a season-ending injury to a player on a big expiring contract who the team doesn't mind trading because they don't care about having his Bird rights.
As a big expiring contract, Humphries is perhaps most valuable as a matching salary if a team is looking to dump a big contract signed beyond next season. The best target is probably a team which has had a disappointing season and is planning to shift into rebuilding mode (i.e. tanking) but has a good player signed to a long-term deal who they think is too old to be on a team that is rebuilding. It could happen, but it might not.
There's a decent chance that the Celtics young players will be progressing so that after this season, Ainge will be looking to add actual players who can contribute now rather than future assets such as draft picks, so I don't think the Celtics will be in the market of trading Humphries for a bad contract and future picks that are unlikely to be one of those coveted 2014 first rounders.
Additionally, since Humphries is an expiring contract and most outsiders looking in on the Celtics will probably think that it doesn't make sense for him to be in their long-term plans, teams that might be interested in Humphries are probably going to wait to see if he gets bought out. Teams that might want to deal for him are going to be those teams interested in being able to re-sign him to a new (and smaller) contract next summer. The rumors that AInge is interested in Humphries beyond this season may just be posturing to make teams think that they can't wait for Humphries to be bought out.
I just don't think it is likely that there will be good deadline deal for Humphries. I'd be more optimistic about being able to get something of value in return for Brandon Bass.
So, I think it might be more likely that Humphries gets bought out after the trade deadline rather than he gets traded before then.