How can I get my (rather large) boyfriend a plane ticket?

My boyfriend is 6’6 and is built like a lineman. He has extremely long legs. I wanted to buy him a plane ticket from a discount plane ticket site (which I have used for myself before, but not for him.) I know his legs would be too long to sit in a normal seat. Even if I buy the ticket offline from like Priceline or something, can I make it so that he can sit near the emergency exit door? We will be using Sun County Airlines. Also, his shoulders are extremely broad and I fear that will make it so we have to pay for 2 tickets instead of 1. Is there any way to avoid these complications or spending extra money?