Question: I'd like to route my multibit traffic through TOR, but have been unsuccessful finding out if it's possible. It's certainly not in the GUI settings on OSX.

Answer: 
Unfortunately there is a library used in MultiBit/ bitcoinj for networking (called netty) that does not support SOCKS proxies. Thus currently you cannot set up MultiBit to use Tor.

It is something we want to support so there are plans afoot to refactor the code and use a different networking library that does support SOCKS proxies.
As it relates to Bitcoin, no. Bitcoin is a peer to peer network for sharing the transactions and would require some server out there running TOR to convert the rest of the network to the same TOR and redistribute the transactions. I have not heard of any plans of implementing this in to Bitcoin transactions of any kind. If, on the other hand, your multibit traffic is not a virtual currency, I would recomend checking port forwarding settings on the application to local host 127.0.0.1:(port) and see if the GUI can allow that.