So against my better judgment, I bought vorpX.
It's a bit of a mess to get a game running, and I hate it when it tries to make a game something it's not (aka turning a game designed for a screen into a game that can be played as a "full fat" VR game), but the theatre mode is exactly what I wanted out of a 3D conversion.
Take a game, stick it on a big ass screen, make it 3D. It's pretty awesome. £35 is a lot for just that, but you know what? It works. On some games. I definitely recommend giving it a look, because the extra depth of your games in 3D is pretty cool. It kinda reminds me of how excited I was by 3D on the 3DS back in the day.