You can do Blind retrieves as a way of teaching a solid straight go out. This also helps with directed retrieves. Some trials don't have baby gates or center posts to go out too. Some people might be against blind retrieves because the dog doesn't always get to retrieve something and gets told to do something else part way through, but as an example we do this type of thing in drops and heeling with out problems..
We use a target, at least until the dog remotely understands what you want with the command. I think you have to give them a way to reap a reward. If you are sending the dog to nothing, how can you reward when they get there?
We use a hoola hoop. Trained up close with a ring gate in behind. Then we move further away as she's getting right in the hoop. She gets the visual of going to the gating, and the hoop is only a physical place I can tell her she's done right by going in.
I am still running after her, and treating her when she sits facing me in the hoop.