Removing the top piece of dynamat (the one in the top quarter) or alternatively, cutting a strip of felt in the same shape and covering the top quarter with it (still leaving the dynamat in) should do the trick.
I feared the cable might have made a difference... so the mod had to be performed on a stock pair. But you can definitely play around with the dampening and get very interesting results.
For instance, if you'd like to color the midrange, you can try stuffing different materials right where the circular piece in the middle is... or stack more leather and felt for a thicker and bassier sound. You can play around with that more to customize for your own personal taste. Myself, personally, I have a lot of dampening in the back, and it all gives a very nice strong bass presence with a clean and clear midrange.
The ES10 turns out to be a very transparent headphone, so every little change would make quite a noticeable difference. And it can sound very very good.
My ES10 is now tuned to be so transparent that a non-audiophile can detect the difference in the headphone out port of a 2011 MacBook and a 2012 MacBook. That happened just a few days ago, and it totally made my day when he went like "oh wow, how is that possible?"