Basically. i think they chop the ront off of the cocker...after removing the front block..they cut off the bit that the barrel rests on, then put a special front block on, with a different vert ASA on it.
Probably...
I think thats basically it. They chop a certain amount off the front of the body and instead of the usual seperate ASA and front block, the ASA comes out the plugged up hole at the bottom of the front block, or you can buy front blocks with ASA's built in.
Look at the Dye minicocker, you will see the ASA comming out of the front block. http://www.dyeprecision.com