I had a look and as I read it, it is a global solution.
Given that the machine gets it's files from USB sticks as well as the network and people transfer files to that machine for playout it is not the answer to hide all USB devices. It may be that what I ask is impossible.
One solution I had in mind was to have a background task running from the USB HDD so that anyone who tried to remove from the sys tray was prevented, physically they have no chance. Knowing them as I do (it only takes one) they will assume. And not see they have asked to remove the wrong device. That will eventually result in someone yanking out their stick before it is ready. They would learn - eventually.
The only problem with that is that someone else who thinks they know, will stop the blocking task. Perhaps I should call it "DO NOT STOP THIS APP".
As one person put it to me and you can see where it applies.
The arrogance of ignorance.