How long has he been sneezing?? Could there be something in his nostrils (dust/dirt) ?? I'd keep watching him very closely for any other signs of problems. Watch for swelling of the head, crusty eyes, coughing/sneezing of blood etc. Is the hen showing any problems?? Without there being any advancement of the symptoms it's hard to know what it is to treat, so I would continue with what you are trying.
I really hope he is not sick, but he could have one of any number of upper respiratory ailments, such as Infectious Coryza, Infectious Bronchitis, a CRD, or perhaps some other form of respiratory distress including bacterial, fungal, or viral infection.
Just don't panic, play it smart. I would leave him and her in quarentene for several weeks and then put another chicken in with them for two more weeks to see if begins the sneezing. Yes, it's a pain in the behind. But, you just don't want to expose your flock to something you will regret. They could be carriers to something and you never even see symptoms other than this sneezing.
Congratulations on finding a nice, sweet roo. I wish you many happy years with him.
Claudia