Last night, I figured out the mellotron parts for "Brief Candles." Or at least I think I did. I think there are mellotron parts throughout the choruses, which I hadn't noticed; I'd thought they were just in the bridge. I used the fake flute setting on my keyboard, which I think has a bit too much tremolo to sound mellotron-like, but it's the best I could do. I've been thinking about getting a Nord keyboard so I can use their mellotron samples, but I don't have the money for it yet (and probably won't for a long time). They also have Hohner Pianet samples, which I could definitely use. They even list the Zombies under famous uses of the Pianet.
I still don't know very much of the piano part (so a lot of this is empty space), and I still have to record what I know with two tracks because I can't play both parts at once (so they don't match up perfectly).
But because I learned the mellotron part, I think I now know all of the mellotron parts on Odessey and Oracle ("Care of Cell 44," "Brief Candles," "Hung up on a Dream," and "Changes"). What I know for "Hung up on a Dream" might not be too accurate though. (There's also the un-used mellotron part for "A Rose for Emily," but I haven't gotten around to learning that yet.)