Update - We released Willie this morning. I planned to let him go in one of my customer's front yard (with her permission of course!). It's an amazing yard, full of pine and apple trees and a lot of other sparrows. However, he must not have been as timid or tame as I thought, because he squeezed out of my hand and flew across the street into a tree as soon as I took him out of the cage.

Hopefully he will enjoy his freedom and be ok. Good luck, Willie!