no how to or anything, but i did put some pics together so you can see the guts. basically a 2" cylinder attached from say his stomach to his crotch. a spring on his spine so he can bounce back. not the most professional job but i think he'll do. a puppet master controls the whole jerking motion. tap the button to however you want it to go and it repeats what you put in.
http://img72.imageshack.us/my.php?image=im000946lg1.jpg
http://img72.imageshack.us/my.php?image=im000947ym9.jpg
http://img72.imageshack.us/my.php?image=im000949lc8.jpg
http://img72.imageshack.us/my.php?image=im000948wj2.jpg
http://img72.imageshack.us/my.php?image=im000950kx4.jpg
http://img72.imageshack.us/my.php?image=im000951fe0.jpg