I think it would weaken his position significantly if he were paid...
http://www.ieeeusa.org/members/IPandtheengineer.pdf
Check out page 5. If you are an employee of the company the company clearly owns your work. If you aren't getting paid though and there are no other agreements covering your relationship... ...You could argue you were never employed and your work still belongs to you.
The other big question would be whether or not you used employer resources in a significant way.