Have you experienced success using an Exit Intent popup with a 1 field 'email address' form fill? I've tried it twice and did not generate any form fills.
In general, I don't find this to be a great practice. What I like to do if you are trying to capture leads is to take the average time of page visit (from google analytics) and then use that to deploy a sidebar popup with more relevant content. I've had better success that way.