Are you in the current situation?
Computer A is connected to the same physical local network as the NAS drive is. It has the NAS drive mapped as a Network Drive. Let's assume the NAS is mapped as a network drive, to the letter W:
Computer B is on a separate physical network to the NAS drive, but can see Computer A via LogMeIn Hamach.
If the above statements are true, could you not just either:
1) Enable Remote Desktop on Computer A and then use Remote Desktop to connect to it from Computer B. Then you can control it just as if you were sitting at Computer A.
2) From computer B access the NAS drive by typing the following into the Run command, Windows explorer address bar, etc: \\ComputerA\w$
Replace Computer A with either the IP or Name of Computer A on your network.
I have assumed above you are running windows, but the same general steps should work if you're on Linux or Mac...