Stacking polarizers
 

Anyone have experience stacking polarizers to make adjustable ND filters?

I know if you attach a Linear polarizer infront of a Circular polarizer and adjust the linear, it acts as an adjustable ND filter much like the Singh Ray Vari ND for a fraction of the cost. But will this work if the CPL goes infront of the LPL? or does it have to be behind it? reason being is i want to get a B&W slim cpl which doesnt have a thread infront to attach a linear pl to. Any experience?