Use a fake identity (create one just for kinky play where you subscribe to your favourite porn or cams or social sites under another name) and somehow allow your blackmailer understand it's not your real identity. If you give access to your fake email she/he will easily figure you are doing that.
If the blackmailer has no problem with, then you are on the right track. He will just mess with your kinky social stuff you have there. If he wants more, run like hell, you really don't want to expose your life to a stranger who can just make fun of you ignoring consequences!
Worry about the photos and the sites where you might get published. Try an agreement at start, with a cancel suggestion like a safeword. There is nothing legal you can do in this matter but at least you can agree on some rules hoping they will be respected.