Julie said something like: "Tune in next Thursday to see if Matt uses the POV and who gets evicted" so it seems he'd stand up immediately before voting starts. The brigade is worried about Matt's "brilliant" ideas so they wouldn't be happy if he pulls it out of nowhere after lying about it. There's nothing in the rules that we know that prevents him from saying something about it.
Also, it seems the HOH and POV winner would be safe from Matt's POV. Not sure if someone saved with the POV could be U-turned right back into the seat but I doubt it.
As for Ragan's sabotage efforts, he still had to make a choice and then find a way to apply it. Up to now, he made the safest choices and he has caused paranoia. What else do you want him to do? I'm pretty sure that using dynamite to blow up the house, however desirable that would be, goes against the rules.