Найду железку — протестирую
access-list 104 permit tcp host 192.168.1.111 eq 3389 any
ip nat inside source static tcp 192.168.1.111 3389 interface FastEthernet0/1 3389 extendable
ip nat inside source static tcp X.X.X.4 3389 X.X.X.20 3389 route-map nonat extendable