Just like my last job. . . No internet, that is.
Well, the link I provided the second time is a registry tweak. I'm pretty sure regedit.exe is locked out of most users if they're not the administrator. OTOH, most users may not even know it exists. This would provide a solution to locking the homepage, and not allowing anyone to change it.
Of course, back up the registry, blah blah blah. . .all that stuff you already know so well.