Instead of beefing mine up as much as his, I wanted to add a thin layer of reasonably-dense foam. I had a spare yoga mat laying around. It's a very thin one, and has a light stippled pattern. My assumption is that if one layer of it keeps me happy for an hour while doing yoga, four layers of it should make my bottom much happier during a long ride.
In particular, I was hoping to feel the springs a little bit less and disperse the pressure throughout my seat.
I cut four layers of the yoga mat and laid them between the plastic sheet and the original foam. This has made my seat significantly more comfortable. It took about 20 minutes from start to finish, took no tools except for a pair of scissors, and was a fun way to end a session in the garage.
The original seat.
Removing the top took no tools and just a couple minutes.
This is a $16 Gaiam yoga mat. Namaste.
The four layers of yoga mat on top of the plastic sheet. I kept the original foam as well.
The final result looks similar to the original. Note a slightly overstuffed line. It is more comfortable.