I have not, but I have a lead for you to follow atleast.
You CAN run multiple windows by using he "-newwindow" command after the .exe file.
The problem I ran into however is that the exe does not connect properly if you just run it directly, and if you launch it normally via the launcher then the .exe is detected as altered and is the command is removed.
So running ore than one window was simple, but it does not connect properly when you run the .exe directly.
Thats as far as I researched into it however. I run one client on each of my systems instead since i have multiple comps that can handle vanguard anyway. Let us know if you find a solution however, as I am sure many would like to know.
I am sure there is a way to get the .exe to connect properly if you just delve into the issue.\ Maybye you should even ask sigil? The -newwindow command was given from them, so obviously they don't seem that adverse to people running multiple clients on a single system. Officialy gamesupport might actually be able to give you the answer
-Stigma