You should be able to use "accessibility" features to bring up a soft keyboard (or just cut and paste from known things) to run the entire attack as a normal-appearing HID mouse, which just happens to be evil. No need to reconnect via a hub; you could do the whole thing within a mouse controller. Bonus points if you can manage to fit all the logic in the same processor/memory the thing includes by default, or something which looks like the same physical package and thus passes a non-destructive open-device analysis.

(which is kind of terrifying if you think about it; almost no one checks the provenance of "dumb" devices like mice. Keyboards sometimes get a tiny bit more scrutiny due to hardware keyloggers inside inline, but that's about it.)

The ultimate solution is a trusted supply chain and equipment which is tamper-evident, non-counterfeitable, and which can securely attest to intactness and provenance; x9.9 pinpads and hsms. But no one does that for general purpose hardware.