Windows Server 2008 R2 includes a new utility named Djoin.exe that lets you join a computer to a domain without contacting a domain controller during the domain join operation. The computer is domain-joined when it first starts, so no restart is needed as with a normal domain join. The computer where you run djoin /provision and the destination computer both need to run Windows Server 2008 R2 or Windows 7 (download).

More info: TechNet (step-by-step guide)