Have you searched under the old standby of mother's maiden name? The ideas such as the father's mother's maiden name?, reversing the forenames, using common alternative spellings such as Dougherty/Doherty, Brown/Browne, Smith/Smyth ect etc. Then there are the ones who registered using older brothers or younger brothers details
Could you pl give us his actual name, dob etc so we can have a look. There are some pretty good sleuths on here.