Can I use the projection matrix to calculate frustrum corners?

I have an image effect that is needs to be applied differently in each eye - basically it adds a vertical gradient between two y values in world space. I used some code from GlobalFog and got it working, but there is a problem when the player tilts their head - the gradient moves up in one eye and down in the other, and it's more pronounced the further away it is. I've figured out that it happens because the projection matrix is different for each eye, for example in the vive it is:...

Can I use the projection matrix to calculate frustrum corners?