OSX Emacs: unbind just the right alt?

Question

I'm using emacsformacosx.com and would like to stop the Meta_R (right meta, or right option key) on my Apple keyboard from being an Emacs meta key.

The reason is that I want to be able to continue using the right option key as a character modifier so that I can enter UTF-8 chars when writing in emacs. I know I can do a C-x 8 RET and type em dash, for example, but that's a lot more work than Alt_R -!

Is there some way of passing the keycode to global-unset-key? Or something else I'm overlooking?

I should be clear that I still want to be able to use the Meta_L binding :)