Bisley state on their site that "compressor plates" are compatible with their filing cabinets.
However they cost £30 each. eg http://www.officeallsorts.co.uk/bisl...k-5-code-bscp5
I find that a few glossy magazines at the front of a draw and also makes it possible to read the folders right at the front .
Next I use a small (8cms) cardboard box to put right at the back, since the last few inches of the draw is difficult to access otherwise.
Then an empty ring binder (spine facing down) in front of the cardboard box is good for angling the folders for easy reading if the draw is low down.