In C:\Games\Piranha Games\MechWarrior Online\User.cfg
Dump this code in and save it:
r_stereomode = 1 r_stereodevice = 3 r_StereoScreenDist = 20.00
Restart MWO and head to the settings options.
The ability to turn on 3D vision in the game setting will be activated.
You can't adjust convergence settings with the keyboard, it's done via r_StereoScreenDist (which is with this config currently set to be ~30 ft in front of your mech). I like a high convergence with my 78" screen, your mileage may vary. If you do make adjustments, you need to restart MWO from scratch to try them out.
Feedback for the devs:
I appreciate how cool the helmet elements all bend outward into 3D space around your vision. The targeting reticles don't necessarily need to scale into the distance based on what they're pointed at, but they need to, at a minimum, be pushed back further into the screen, perhaps centering just past the cockpit.
Also, it's obvious now how much cheating was done for the cockpit since everything goes flat. For a better 3D vision rating, the whole cockpit should be done in 3D, otherwise it doesn't scale in and out of the screen correctly.