Apply GP User Settings to specific Computer Accounts

Hi, 

I need to apply GP user settings to all users that login to computers within AD but this needs restricted to computer I specify.

Using loopback processing, I can get the user gp settings to apply the computers within the OU's fine, but I cannot control which computers in the OU get this applied to.

Can anyone help?

For example, I was to set a GP at the top of the AD tree, which contains user settings, but I want to restrict these user settings to apply only to specific machines?

Thanks