Given that the body is not resting on anything - you can work on both sides at once.
When you have a set neck - easy solved - I find a well placed quickgrip with some wire and suspend from the roof / ceiling / whatever. Gives you a handle for the guitar as well.
I'm not sure what you mean about "a well placed quick grip" Brendan. Where can I clamp a quick grip on a guitar body to allow me to finish all sides at once?