By far the easiest way to enable the Administrator account on client machines in a domain is to use Group Policy, here is how you achieve this.
I am assuming you have the basic understandings of applying/creating Group policy settings on a Windows Domain, if not, leave a comment and i will see how i can help further.
Go ahead and open “Group Policy Management”, for testing purposes, it may be worth creating a new policy on a test OU, and placing some test client accounts within that OU. So Right click your OU and select “Create a GPO in this domain, and Link it here”. The new GPO pox will prompt you for a Name, so go ahead and give it a meaningful Name, and click OK.

