I think this, the Cowboys are still trying to trade Kenyon Coleman, that will create one open roster spot.
Other position that I think the Cowboys will trade a player is Fowler, true he is backup deep snapper for kicks and punts, but you can find those guys.
So, if a teams DE in 3-4 goes down or a linebacker goes down I see the Cowboys trading coleman or fowler, maybe both.
Then, if Vandy, the goofy kicker ever gets his act together and can kick off decently, then that will be another open roster spot with cutting backup kicker, I dont think that will happen till the 4th game or later, when Marcus Coleman comes back, if he does.