Well, what they said isn't actually outside the realm of doable if you're clever. Since they said you can have multiple characters online and following one character, the hard part is done. That's permission.

The restriction is that one keyboard button press or one mouse-click must equate to one single action on one single character, and each character needs to be controllable with its own respective keyboard and mouse. It also doesn't say that you can't use 3rd party software to launch a game window, just that each character must be controllable without using it.
That's what they say, but the reality is that in games with this sort of rule you're immediately suspect if you're multiboxing at all. You're at risk of being banned based on player reports simply for appearing a certain way. They also cannot tell the difference between whether you're using a hardware setup or a software setup if your keystrokes appear to be synchronized, and it wont matter if you're using a round-robin sort of setup either.

See Guild Wars 2 for example.