Whipped up a quick function to do that:
 Code:
Function RemoveFromLocalAdmin($userName)
  Dim $WMIgroups, $obj, $adms
  $WMIgroups = GetObject("WinMgmts:root/cimv2").ExecQuery("Select * FROM Win32_Group Where LocalAccount = True")
  For Each $obj in $WMIgroups
    If $obj.SID = "S-1-5-32-544"
      ? $obj.Name
      $adms = GetObject("WinNT://"+@WKSTA+"/"+$obj.Name)
      If $adms.IsMember("WinNT://"+@LDOMAIN+"/"+$username)
        $adms.remove("WinNT://"+@LDOMAIN+"/"+$username)
      EndIf
    EndIf
  Next
EndFunction


You can edit this function easily to use it for remote machines, I don't have the time anymore ;\)