Help me with a Headphone Mod

So in December I received a pair of Sennheiser PC 350's to replace my AD-700's, which had zero noise isolation. I am OCD and ANY background noise that isn't coming from my desired audio source annoys me to the point of frustration (human voices, fans, etc.). I can't exactly cover my bedroom walls with 6 inches of foam either.

Now to my problem. When I first got these they fit tightly around my head and I was satisfied with the noise isolation. Now they are a bit looser, and there is no longer a seal around the bottom of the headphones, near my earlobes. This has also caused a loss of bass, and I listen to lots of old hip hop and rap so I like my bass. 

So I am looking for a way to tighten them, I guess? I was thinking about using some sort of elastic band around the top of the phones, where the headband attaches to the earcup. What do you guys think? 

Also what are some other noise isolation mods? I have heard of putting clay inside the earcup? I have disassembled headphones before and I'm not scared of voiding a warranty (I void warranties for fun >:]).

If you help me with this, you might save the lives of my two younger brothers. 

Check out this for modding the 350s. http://www.head-fi.org/t/406187/modding-the-sennheiser-pc350-headset

I may try that, but I am more concerned about the lack of a good seal around me ear due to the headband becoming looser of the last couple of months.