Here is the setup in my basement gym. I already had the squat rack built a long time ago. I picked up the bench at a garage sale for $5. I have a couple pieces of carpet between the bench and the rod on the right side. I have a foam pad folded up underneath a towel for extra padding and to get a few inches extra height. The blocks under the bench on the left are blocks I made out of 4x4s for doing pulls and deadlifts from just below the knee. They worked out to be just about the right height for this.
Next I attach some weight to my legs. I am use 2 25lb plates here. I run a belt around each leg and through the center holes in the weights. I also fold my sock down to make it a little thicker so the belt doesn't dig into my ankles so much.
I have the weights secured as tight as possible. I punched a couple extra holes in the belt at the right distance. NOTE: You will end up ruining your belt using it this way, so don't use your only dress belt. I used a belt that fit me when I used to have a 32" waist (I don't think I'll be needing that belt again!).
This is the starting position. I have to get up on my toes to get onto the bench. As you can see, there is a good stretch on the very lowest vertebrae of the back, which is the main benefit of this exercise.
This is the finishing position. I like to bend my knees a little. It keeps the stress of the knees and also keeps me from hitting the wall with the weights or my feet.