Keyboard key for Captions

I recently purchased a SofaBaton U1 remote which has the option to use macro keys. I would like to be able to program the remote to mute my TV and turn on captions. So I would like to request a keyboard key to turn captions on and off.

Edit: looks like keyboard key 'c' turns on captions. But it seems like you can't add a keyboard key to a macro unless I'm mistaken..?