P3D De-polarising filter?

["gl@xxxxxxxx" <gl@xxxxxxxxxxxxxx>]

I've finally gotten hold of the lenticular screen I'm planning to use for
polarised PC 3D projection using my two LCD projectors.  Watching a single
projector's output on the screen with polarised glasses however has revealed
what should have been obvious (with hindsight) - ie. that the light from LCD
projectors is already partially polarised!

Well, from my (limited) understanding of LCD technology, polarising filters
are used on both sides of the liquid crystal layer, so of course the emitted
light is already polarised.  In practice, this is causing a marked colour
difference between the left/right eye images of a single projector as seen
through the glasses (I think the reason that the difference isn't more
drastic is to do with the beamsplitting that's going on inside the
projector).

The point is, although it looks like I could compensate for this colour
difference, I'm obviously loosing light output once the projectors get their
polarising filters attached, and they are dark enough already for this to
become a problem... so, the question is, is there such a thing as a
de-polarising filter?

The idea is to insert this between the projector lens and the polarising
filter, to get the max lightoutput before the intended polarisation occurs.
So, do they exist, how about in convenient filter form, do they have an
adverse effect on image quality, and, most importantly, where could I source
such a thing (in the UK)?
--
gl