You have a machine that is not a member of your AD domain but you want to manage it remotely through the Computer Managment MMC (compmgmt.msc).
Manually create a connection to the IPC$ share on that machine using net use, then you can connect like normal:
C:> net use \computername /user:computernamelocaladmin The password or user name is invalid for \computername.
Enter the password for ‘computernamelocaladmin’ to connect to ‘computername’:
The command completed successfully.
Now you can launch compmgmt.msc to manage the remote PC.