Um servidor Gateway de Área de Trabalho Remota fará o trabalho para você. De aqui :
Remote Desktop Gateway (RD Gateway), formerly Terminal Services Gateway (TS Gateway), is a role service in the Remote Desktop Services server role included with Windows Server® 2008 R2 that enables authorized remote users to connect to resources on an internal corporate or private network, from any Internet-connected device that can run the Remote Desktop Connection (RDC) client. The network resources can be Remote Desktop Session Host (RD Session Host) servers, RD Session Host servers running RemoteApp programs, or computers and virtual desktops with Remote Desktop enabled. RD Gateway uses the Remote Desktop Protocol (RDP) over HTTPS to establish a secure, encrypted connection between remote users on the Internet and internal network resources.