Please realize that his lack of being potty trained at night has nothing to do with his willingness to be potty trained at night. It is purely a biological issue, not a behavioral issue. (There's another question about this a little further down the page with some very good responses - you may want to take a look at that.)
That being said, just put him in a diaper at night; the most absorbent one you can find, and let your child get the rest he needs at night. Nothing you or he can do will make him be dry at night before his body is able to release the enzymes that signal the kidneys to stop urine production at night. That is the key to staying dry all night (not making him wake up to pee, or not letting him have water before bedtime, etc). Some children don't develop this until they're 7 or 8 years old, and that is considered totally normal.
My older daughter was potty trained at 24 months, yet couldn't stay dry at night until Kindergarten. She was so mad about it, but we just kept telling her, it's okay, your body just isn't ready yet (and then baby sister was potty trained and happened to be able to stay dry at night - before big sister! Drama! ;)
Just use whatever works for now, and forget about it. He'll stay dry on his own at some point soon.