Open to suggestions, maybe?
As an alternate, have you thought of going a bit more elaborate but easier in my view? I often use Java fern on wood as a way to build a quick cover for things like tubes for filter, heaters, etc. and find super gluing a bunch to wood is quick and easy if I have the plants on hand. since a matten filter if just a nice place for lots of bacteria, I might think adding a "semi-woven" screen of small branches like off cedar might let you come close to covering the filter and make a bit more bacteria living space at the same time?
One problem I might see with adding the plants directly to the foam is that the roots do burrow through foam and keep growing which does tend to cut flow. Once the roots are in the foam, they are there forever!
The big point folks often jump on is that cedar is poison! But that is almost always from folks who have soft water and/or have never actually tried it! They just don't think very far!
The part of cedar that is a hazard is the sap/moisture content, so if we get wood that is old and all the sap is gone, combined with hard alkaline water, having lots of buffering quality, we don't get the problems. Often the books are written on the East and West coasts where the water is soft, so that it doesn't fit what the middle of the country finds.
Lots of free twigs and small branches that weave together nice if you go for a walk in most any part of our "cedar alley" ? Just get the really dry stuff and go for it as cedar works well for me!
Want to play " find the heater/ find the filter" ?