I would utilize fastpass as much as possible but I think you may be able to get a GAC for the alternate entrance use. This way if he needs to run out quickly he doesn't have to fight through a long line and crowd.
Alternate entrance is not always available, and can be just as congested - you can't count on it.
Unless you meant you wanted one ahead of time. In that case, if you cannot locate one online, you can always call guest services and ask them to mail one from each park for you.. also get the DTD one as well, you may need a restroom there too