I hate to simply state the obvious, but if you ask for a recommendation from your EVP, what guarantee do you have that your EVP will give you a strong recommendation if he knows you will leave the organization? If he knows that you will leave the organization, then he may decide to dedicate less time to the rec and put in less effort.
On the other hand, there is no better reason to leave a job then to go back to school. Perhaps you can have a discussion with him about how you would love to keep your relationship with the organization and that you would strongly consider coming back upon graduation?
EDIT: In re-reading your post, I understand that you would get fired if he found out you were going full-time...guess your only option is to try and find another recommendation.
I appreciate the kudos if you find this post helpful! +1