Edit Windows Update GPO Via Command Line

You could use PowerShell to update group policy. Here's an example:

set-gpregistryvalue -name "WU" -key HKLM\Software\Policies\Microsoft\Windows\WindowsUpdate -ValueName "WUServer", "WUStatusServer" -type String -Value "http://wsus01.internal.local:8530"

And here's where you can read up more on the amazingness that is powershell:

http://technet.microsoft.com/en-us/library/ee461027.aspx

OR AN EVEN BETTER ANSWER:

Step 1: Setup Active Directory
Step 2: Join computers to Active Directory domain
Step 3: Configure group policy to point computers to WSUS server
Step 4: Profit

Most of the Windows Update settings in Group Policy are set at the Computer level, not the User level. Also, there's no need to be leery of doing this directly via the registry. That's the only thing Administrative Templates in Group Policy actually affect.

All of the "Windows Components\Windows Update" settings are stored in these two keys:

HKLM\Software\Policies\Microsoft\Windows\WindowsUpdate
HKLM\Software\Policies\Microsoft\Windows\WindowsUpdate\AU

The "Specify intranet Microsoft update service location" policy in particular sets the following values:

• WUServer (REG_SZ in the root key)
• WUStatusServer (REG_SZ in the root key)
• UseWUServer (REG_DWORD in the AU key)

It's easy enough to see exactly what gets set by manually setting the policies using gpedit and then looking at what changed in the registry. If you're feeling adventurous, you can also crack open the actual administrative template file to see what's going on. On Vista+ it's WindowsUpdate.admx. I don't recall what it is on XP and earlier, but it would be a .adm.

*Edit: Apparently it's not clear whether the OP is trying to script local policy settings or domain policy settings. This answer is specifically for editing local policy settings on a single machine.