Replacing Sennheiser Ear Cushions

On my Sennheiser HD580 headphones, the thin film of foam which covers the driver has worn away on both earcups. Is there any way to obtain replacements without having to purchase the ear cushions as well, or do they always come packaged together?

Also, I cannot seem to figure out how the earcups would disassemble to make replacement of the foam films and/or ear cushions possible. Is this hard to do?

Thank you for any suggestions.