I DM an irl game, and use the flatscreen/roll20 combo for fog of war. As Andrew suggested, I run roll20 on two browsers, and duel screen between my laptop and the tv with an hdmi cable. The tv screen has me logged in as a player, and I log is as the GM on my screen. Works perfectly to do fog of war, shuffle map screens, and move icons. We also have clear plexiglass over our tv screen for dice rolling and dry erase marking. It's an excellent combo of tech, minis, and map marking.