I checked this out years ago for our first WDW trip. I found it easier to drive, if you can. It would take 20 minutes that way.
I don't know if the same is true, but I would have had to take a WDW bus to specific location, then switch to a city bus. Just seemed like a lot of trouble in the long run.
I do not know where the Lynx bus drops off USO guests.
You may want to ask this on Transportation Board too.