Don' reckon PP's gonna legalize your babies here, but wot you can do is make these custom models and use em as existing units.
Like me own character Christoph'/Kristov and his trusty golem Binki-Ball are used as a GreyLord Koldun Lord (to represent Christoph's arcane talents and marshalling skills) and a Devastator (As that is the chassis Binki-Ball was styled after)
/makes it a lot easier and that way ye needn't fear balance issues.
They are major characters in my Warmachine novella The Sword of Morrow[link] Go ahead and take a read and you'll get to know the characters better. If you do end up field testing them I'd love to hear how they play out for ya.