I'm sure I speak differently about categorical imperatives than Kant does. I haven't read much of Kant, and I don't regret that. In your language, what you call an "end in itself" is what I mean to pick out when I talk about an imperative that "holds... regardless of any stated [arbitrary, desired, subjective] ends at all." I don't really know what it means for something to be an "end in itself". Kant's idea seemed to be that we ought to do X regardless of what anyone wants. Your way (and perhaps Kant's way) of talking about this is to say that we ought to do X regardless of what anyone wants because X leads to a particular "end in itself", whatever that means.

your reduction of hypothetical imperatives assumes that effective means to one's ends ought to be taken, and this assumption is also a form of cheating

My reduction of hypothetical imperative doesn't assume this. It only translates 'ought' into a prediction about what would realize the specified end. If there's something mysterious left over, I'm curious what you think it is and whether it is real or merely a figment of folk wisdom and linguistic practice.