Would it be possible to replace one of the film polarizers (on the LCD) with a circular polarizer further in the chain (ie: at the triplet)? I'm not sure if this is an obvious optics issue so if it is please correct me.

Short answer. No.
Long answer. You need a linear polarizer. You can put it wherever you want in the light path (with variable results).

See: http://en.wikipedia.org/wiki/Polarization

EDIT:
You might have mixed up the terminology.
If you're talking about a linear polarizer cut in the shape of a circle, then yes, it would work (you have to rotate it to match the degree of the other polarizer + 90).

Hey there.. actually I was referring to a camera circular polarizer (spins freely to accommodate changes in light on the fly - think we're talking about the same thing in different versions ). And yeah, did work. Stripping the AG off revealed that the sheet was a combo AG/polarizer.. nuts. Attaching the polarizer to the projection lens and spinning to accommodate the remaining polarizer (still on the opposite side of the LCD) produced what it was supposed to!

Just a quick, instant & cheap ($15 @ Bestbuy) fix if anyone else makes the same blunder. I'm using the standard 15 set (purchased a couple years ago - finally putting it to use) and the matching filter is 67mm - you'll need to make your own mounting to attach the two (tape works fine).