Are you looking to use the chemical reacting polyfilter pads or just a poly fill "filter floss..?
The "pads" are rather stiff, but could be cut to size, rolled in a tube, and held in place with rubberbands around your "center filter" sort of like the "prefilter sponge" they come with...
Or if your just looking for "mechanical" filtration you can use the "filter floss" in the carbon "basket" and change it out weekly...