Yeah, I mentioned using a simplified notation (still in dots-and-dashes form, though there might be a more efficient way) in a different comment. I actually also mentioned using something like electrical impulses across the small of the back. But then again, that latter one won't really be hidden well (given that this all came about from a challenge of doing chess naked).

There's also the possibility of the accomplice having access to a chess computer (program). But yeah, if the accomplice is better at chess, enough to operate on that level, then why not just have them play indeed?