It's too bad you can't set Network Location specific Internet Explorer\Internet Settings GPOs because that would quite neatly solve this issue. Oh well.
You could then build a GPO that:
- Pushes the PAC file out to client's C:\ so its available to them when they're not on the local network (
User Configuration\Preferences\Windows Settings\Files)
- Configures Internet Explorer to use it (
Configuration\Polices\Windows Settings\Internet Explorer
Maintenance\Connection\Automatic Browser Configuration)
I should also mention that many OEM's provide 3rd party tools to do "Network Profile" management. I believe Dell had one called Network Connection Manager that was bundled with their NIC drivers, although the inability to centrally manage it made it a non-starter in our environment. There is likely other paid 3rd party applications that provide Network Profile/Location-specific management of these settings.