So, from your outline of your goal, you should be able to do this by using rules AND configuring the Patch Manager Automation Server.
- take a backup/snapshot of the system (just in case)
- Go to Patch Manager System Configuration -> Patch Manager Servers and run the "Patch Manager Server Wizard".
- Choose the option to "edit an existing patch manager server's configuration settings"
- Choose the PAS (main patch manager server) from the dropdown and hit Next
- On the "associate a patch manager server...." page, make sure this server is associated with a Management Group (most environments only have 1 to choose from) and make sure that the box for "Include this Patch Manager server in the default round-robin pool" is CHECKED, then finish the wizard.
- Run that wizard again, but this time choose the other Automation Server from the dropdown, and make sure it is also associated with a Management Group but also make sure that the box for "include this patch manager server in the default round-robin pool" is NOT CHECKED, then finish the wizard.
- Next, go to Patch Manager System Configuration -> Management Groups -> [your management group name] and then select the "Automation Server Routing Rules" tab.
- Create a Routing Rule for the other site (most likely that would be a subnet rule, but it could be based on something else) and choose the remote Automation Server. When you're in the wizard to define the rule, you have the option of making it an 'absolute rule' which would mean that it would not try to use the Automation Server on the PAS if this Automation Server is not available.
I think that's all you should have to do. If I'm thinking about this correctly, Tasks that are targeting everywhere BUT the remote site should get caught by the default pool.. but Tasks that are targeting machines in that subnet should hit that rule and be directed to that remote auto server. If you choose to try it i'd be curious how it works out for you.
Thank you. I will give it a go this weekend and reply back status.