Help trapping bass leak.

[GL Respect Due]

I live in a duplex/town house. My studio is in my (1) car garage. I've successfully built a floating wall and sealed the garage off so now I have virtually no leakage from the garage door. Unfourtantly, one of the walls in my garage is shared to split my neighbor and I's garages. Given that the wall seperates (2) garages, it's packed with fire code specifics (I'm guessing maybe 2 panels of sheet rock per wall side plus r25+ grade insolation?) Anyhow, high frequency leak is pretty much nill.. but the lows of basslines and kicks leak through. I'm basically looking for a ghetto solution (cheap solution) to remedy the bass transfer. I know without some fancy construction work (building another wall in front of the wall) i'm not going to be able to completely stop leak.. but I want to do what I can to maximize the bass leak. I'm even open to suggestion that might not be mixer enviorment friendly. I'm less concerend about over the top accoustic balance at this point, then I am the leak. Bottomline, help me find a solution to cover a 20 ft long wall with whatever to cause some serious dampening of the bass traveling through that wall!