What about if you use fake blood, if you drip it in a long line (you'll probably have to get someone else to do it for you) whilst you lying down and your fece is horizontal, then you would get a slight 3D effect, just wait for it to dry before moving, as it would probably drip down your face XD
My Brother is doing a Stayne costume and we're gonna use Rigid Collodion for his scars.
Is nice XP
But you paint it on and as it dries, it pulls the skin tigharound it and makeup can cover it well. My only advice is to have a friend paint it on so you can keep your eye closd as it dries. It has vapors that + eyes = Hell!
Good luck on the costume, I'm looking forward to see how yours turns out ^-^
I was actually thing about something like that, But I'm Actually going to have my eye covered with a Foam latex patch, seeing how i was Leaning towards Paint anyways than an actual prosthetic seeing how you have to build up to make a depression in your skin. An I have a Knack For the whole paint thing