Uhh...this sounds like a bad plan. Although I don't know the details, I see these as distinct possibilities:
1) It may change or jeopardize your friendship
2) He won't equate the love of a male with the love of a female, meaning that he won't necessarily take your confession as a sign that he's lovable by those he desires
I think right now, if he needs support, you can provide that best as a friend, not an unrequited lover. The furthest I'd go is complimenting him and telling him about all the great qualities he has. However, in reality, self-confidence can't be given to someone permanently (has to be personally discovered), and it can only be given temporarily if the person giving it is someone seen as personally important (i.e., a woman). It sounds to me like the best plan would be one that would help him discover his worth and a woman who sees that, too.