I recently bought myself an akg-k420 recently for cheap on catchoftheday.com.
The stock ear pads were relatively comfortable but after a few hours I needed to take a break from them.
Just for some experimentation I did pull apart 1 of the ear pads, which is glued to a plastic O ring.
The glue wasn't strong enough so the ear pad came off without the plastic ring.
So I put used a plastic card to stuff the edges back in, and unfortunately the end result was a misshapen ear...