How can a u.s. Citizen help a non us citizen get citizenship if they currently live illlegally in the u.s.?

I have a friend who was born prematurely and litteraly isn't a citizen by a matter of days. He is a bilingual who contributes more to society than I do and he is going to school to be a dr. And I feel that our country would be a better place with him as a citizen. Besides marriage and anchor babies is there anything I can do?