Find or create a policy at the root of the OU of the computers you want them added to, go to computer configuration > preferences > control panel settings > local users and groups
The right click > new > local group and select that action as "update" and in group name select "Administrators (Built in)" and just add the user(s) to the members section at the bottom.
Should do the trick
![Smile :) :)](/styles/default/xenforo/vbSmilies/Normal/smile.gif)
....hopefully