Make sure you have the port forwarded via router (default is 1320) on your SLAVE system and you should still be able to connect, you would just connect to the slave's IP from the ISP.

Edit: This is my Monday so reading comprehension ftl.

Here is a Screenshot showing the connection (No wow's running so you don't see the WoW instance but just the network connection)
Windows Remote desktop from my Work machine to my Home machine (on different networks)