After doing a little reading, I'm not entirely sure a condition node would work anyway as I believe it's directly related to outcolor. Ive used it to create a double-sided shader before and was thinking along the lines that you could use it to make a condition that if facing ratio is 1, make the blinn's reflectivity 0 and if not, reverse it with the reverse node. What gnomon video were you originally referring to? If I have it, I might be able to look it up for you.