Can workstations from completely separate domain access a WSUS server?

I have the situation where there are many workstations in Domain A and a WSUS server in Domain A. The situation is that I want a few computers from Domain B to be able to pull updates from Domain A's WSUS server.

Please assume that there is no link between the two domains (trust relationships) except for a open port(s) in a firewall for communication

Solution 1:

Per Wikipedia

"WSUS does not require the use of Active Directory; client configuration can also be applied by local group policy or by modifying the Windows registry."

This should be possible by setting up a GPO for domain B, pointing to update server on domain A.
Here is a dated, but still relevant article. My understanding, and it's been awhile since I supported a production AD domain, is that it merely replaces the Windows Update Server, as well as providing statistics.

Solution 2:

You could do registry editing to have the computers access Domain A's WSUS.

http://technet.microsoft.com/en-us/library/cc708449%28v=ws.10%29.aspx