The ground crew shut off the external air when I tell them to shut off the external air. Our SOP requires ground personal to be on intercom when HP air is being supplied to the AC. So you did a school 35 years ago - great. A lot of things can change in 35 years, but the value of life isn't one of them.
Finally no, the FTIS does not work with external HP air being supplied on the ground. Then again it doesn't work with internal air being supplied on the ground - in fact it doesn't work on the ground at all, it only operates in flight, but thanks for asking.
You have a great day as well.