Windows Defender Offline Update via proxy with authentication

I have managed to add wims to out WDS server when I need to do a offline scan of a suspected computer. I'm trying to get it to update through a proxy, authenticated. I've tried adding the proxy setting in HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Curr entVersion\Internet Settings\Connections by mounting the boot.wim and loading the software hive. I was hoping for a login box, but it fails. Is their a way to do this? Has anybody enabled internet access in the winpe environment using a proxy?