I suppose you could line the entire cup bottom of your choice with saran/plastic food wrap then spray the stuff in ( spray foams ) and get the exact shape for the fit, then carve away whatever you didn't want or to whichever shape you want. Might work. The outside of that stuff is usually shiny after it dries if i recall, but I forget what the insides are like after you get past the outer layer. Might be nicely full of cavities.
Cadbury Crunchie style holes. There I go again with the Crunchies what's up with that.
Something using the rough handmade large-fibre paper sheets in an accordian fold might do the trick also, never did try that.
I ripped apart a respirator filter ( got charcoal everywhere ) and extracted a circular accordian-style disc made from very soft and delicate paper fibres that looks like an interesting possibility which is why I thought about the handmade papers. A lot cheaper .
Just throwing it out there.
Damn You! I had a brief addiction for Crunchie Bars as a kid, now I've got a full blown jones on for one!
That is pretty much the texture of the foam once you get past the surface.
Could have saved yourself the charcoal mess and bought a cheap automotive oil or air filter.
I'm still partial to the foam though as you could spray it, then push some vaseling coated template/mold into it to achieve whatever surface texture or shape you want. If I wasn't totally obsessed with the incredible sound to be gotten out of 10 dollar Phillips Earclips at the moment I might be tempted to dig out the skullcandy hemis (good lord, watch them start marketing Thant name next, the horror, the horror) and have a go at them and the fujis again.