I think Solus's sole point is that since there is no evidence for the negative (regardless of the fact that you can't demonstrate a negative), he choses to believe whatever he'd like to believe.
Since belief does not require evidence, he can play the lack of evidence against both sides. i.e. "There's no evidence that God doesn't exist, therefore I can chose to believe in God", and "There's no evidence that God does exist, but belief doesn't need any evidence, therefore I can chose to believe in God".
It's an unassailable position.
That pretty much sums it up.