I’ve read about a few ways of doing this, but this evening it occurred to me that using iTunesFS might be really easy and work quite well. Sure enough, load it up, add the new share and you’re browsing and playing your iTunes library.
The only thing I haven’t figured out is how to share this new FUSE filesystem via SMB. It appears that you have to set the allow_other option, but I had no luck getting this to work via sysctl. If you can figure it out, post a comment!