yes it is possible to watch a side by side movie 1 person seeing 3d and one person seeing 2d....
Just DUPLICATE Right lens to Left lens...
In other words... lets say its RED/BLUE style 3d (using filters)... change both to RED or both to blue...
Same can be done with stereoscopic 3d...swap 2 glasses lens...
so that both lens are R or both are L...
u will see the image from a flat perspective