This I do know as I have just done it to my classic.
First remove the cover from the 4 electric motors under the seat. the motor that controls the forward/ back movement is the top one at the front. then undo 1 screw from each side of the motor so that it can swivel forwards. By doing this you can release the 2worm drives without having to unscrew the ends. Then get 2 drills, make sure you can control their speed. Attach 1 to each drive cable but make sure that one is in reverse as the seat will not move evenly. then it is trail and eror as to which 1 is forward or reverse but the seat will slide.
If the seat is high enough to get your hand under you can unplug the motor connection block and hot wire it but let me know if this is any help.