^There's a little bit of confusion there. It's not Welling that says "no tights, no flights". That's the producers. Other characters have flown on the show as has Kal-El (Clark with the human side of him suppressed).
It is believed that Welling is, however, very strict on what he will do for the show. He apparently refuses to wear glasses and limits the amount of time he is willing to spend wearing a suit and tie. He has pointed to negative female fan reaction when he has worn glasses as a reason not to do it. There is very little chance of seeing Welling in the actual Superman costume. The closest we'll get to that is when he wore the Green Arrow costume to help convince Lois that it wasn't Oliver.