Hey bud-
Yeah I 3boxed CoH/CoV for years. It's a pain because you have to do it all manually.
The reasoning I heard behind it (because I tried keyboard emulators and mouse emulators like MouseMachine) is there's hidden character input.
When you type in the CoH/CoV client, there's other characters sent along with your one keystroke, just to make sure people aren't using some kind of bot to control their characters.
You see this sometimes when you're zoning and alt-tabbed out, and you come back to type something and weird stuff happens. Like your character is turning around in circles, or there's a bunch of gibberish on the screen, or you find you've somehow hit the "RUN!" hotkey 19 times in a chat channel.
So a few years ago someone was talking about how it would be possible, but a pain, to look over the code and find a way to duplicate these secret characters. They said a coder could find it but it'd take a few weeks of thankless, intensive work.
In the meantime, I guess our only solution is hardware; an Xzyn-style multiple wifi keyboard/mouse with the same receiver, or one of those splitter devices like Vyndree uses.
-Mac