Most discussions on PAC files are in Web Gateway so have moved this thread there for better support. I can always move it again if necessary.
A PAC file can generally reside on any kind of web server. It there is a place at Google that allows you to store the PAC file then there should not be an issue to do so. Since I am not familiar with Google Apps I don't know if there is such a location. Anyway if you do so you need to ensure that all clients can access the PAC file directly, otherwise they won't be able to fetch it.