Oh well, I was hoping I'd missed something. I'll just keep doing what I'm doing now -- write it in Evernote and then copy/paste when I get back to a computer.
I've found Simplenote on the iPad and Notational Velocity or nvALT on a Mac to be a really lightweight and quick workflow. Plus, there's the added benefit of it all being plain text, whereas Evernote always seems to make guesses about unwanted formatting for me.