I've been able to run three accounts using MultiBox and AutoHotKey. I'd have my main character on my laptop which was running the MultiBox Server. Then I used an AHK script to mirror keystrokes between my secondary instance on my other computer running the MultiBox Client as well as AHK. It worked fairly well once I got everything configured. But I found it really was easier to just run three clients on one system. My framerates aren't that great, but I'm mostly doing PVE, so it's not a major issue for me.