Do you want to add the workstation to an AD-group during OSD so that admin have access? If so, this PS-script may help you out.
$ComputerName = gc env:computername
$GroupPath = "LDAP://CN=ADM_SCCM_Workstations,OU=Groups,OU=System,OU=GMSC,DC=internal,DC=gustomsc,DC=com"
$computerPath = "LDAP://CN=$ComputerName,OU=Desktops,OU=Workstations,OU=GMSC,DC=internal,DC=gustomsc,DC=com"
$Group =[ADSI]"$GroupPath"
$Group.Add("$computerPath")
$Group.SetInfo()
Save the script as a PS1 file. Make sure you put it in your TS after you have network connection and the machine has been added to the domain. Mine runs from a share. Run it with the following command-line: powershell.exe -executionPolicy Bypass -file .\desktops.ps1
If this is not the Script you are looking for, perhaps this may help: http://blogs.technet.com/b/heyscriptingguy/archive/2014/10/03/adding-local-users-to-local-groups.aspx