Need to disable Chrome's "Show as tab" option

Need to disable Chrome's "Show as tab" option

In Chrome, when you open a popup, click the icon, there is an option to
"Show as tab". This is the feature I wish to disable, as overkill as
necessary short of disabling the popup altogether. Using XP Pro SP3.
Edgenuity likes Google Chrome as the browser, and sadly my boss said to
use it. It's a homeschooling site, and we are using it for a Children's
Home for credit recovery and etc. I have to lock it down or else no
schoolwork will ever be done. "Show as tab" gives them a usable URL bar,
which defeats me using kiosk mode. Ideas?
I've already been in Chrome's GPO, nothing there.