You're handling the intersection fine. I like the suggestions of contacting the traffic unit and using a mirror. The traffic unit is unlikely do to much unless there are lots of cyclists, though, since they could sit for quite a while before a cyclist 'causes' someone to impropertly merge into the turn lane.

Also, you could get an Airzound and give a toot to anyone who really cuts you off. If you ride the same route at regular times of day, some drivers will eventually get the message that they didn't have time to pass you. I bet a lot of them ascribe the theory that any pass without physical contact was an acceptable pass.