Central Management Server - Query against host server
I assume that we are indeed talking about Central Management Servers here. And not Master/Target Agent or something else which isn't related to CMS. I see a lot of confusion in this area. Here are a few options:

Skip the CMS. You can register whatever SQL Servers you have in the traditional way (locally) and use a multi server query window (MSQW) for the local server group. Again, I frequently see folks believing that MSQW can only be used with CMS.

Just register the SQL server wherever you want to have it in the CMS tree, but use the IP instead of the machine name. SSMS won't understand that it is the same machine.

Configure an alias on the client, and use that alias name in the server registration. Obvious downside is that all clients where you want to use the CMS list need to have that alias. Sort of defeats the purpose of CMS in the first place.

Perhaps an additional DNS entry pointing to your server? I'm no DNS person, so I can't say if you can have two DNS entries pointing to the same IP.

I'd go for the IP address in the CMS registration. In fact, I did exactly just that a few days ago with a client.