I just ripped it all back off. If you really must.....
Follow the first few minutes of Shivs install for the PROcede uptill the bulkhead plastic piece is off. Once you get there, you can easily access the rear area to plug. Its this...
Trust me, use the cap off a quart of oil when you plug it. Run a lot of tape around the area to plug. Then screw on the cap. It will literally make its own threads and create an air-tight fit.
I didnt really notice much if any sound though.