There has been a recent discussion about managing policy for a Windows Server Core instance that is in a workgroup configuration. This is a little more complex than normal, but here's what you'll need to do to enable Allow remote access to PnP interface and enable control:
1. Configure the firewall on the Server Core machine to all connection via gpedit.
Not being in a domain, the Windows Firewall will have things locked up tight. You will need to enable communication on the target ports or temporarily disable the firewall. For this example, we'll just disable the firewall:
netsh firewall set opmode disable
Don't forget to turn the firewall back on later!
netsh firewall set opmode enable
2. Logon to a Windows Server 2008 "full" system and establish an authenticated session.
a) Logon to a full system and establish a session using net use. The following should do the trick:
net use \\<Server Core FQDN>\ipc$ /user:administrator
3. Create a custom MMC console containing GPEdit.
a) Start | Search | MMC
b) Add Group Policy Editor and point to the IP, or FQDN of the Server Core system.
4. Set the local policy:
a) Navigate to Policy | Computer Config | Admin Templates | System | Device Installation | Allow remote access to PnP interface and set to Enabled