Use a group policy to assign local admin rights you can assign users to the local admins group of domain PC's via Group Policy.
I made a new GPO and named it local admin rights on desktops. In GPO settings goto Computer Config > Windows Settings > Security Settings > Restricted Groups. Add the domain group you want to be added to the local admin group and you're all set.
Don't forget to link the GPO to the correct OU / site /domain.
CT