@blue duck
He's not working off a last, but from a foot cast. It's a cheap form of body casting, you cover the body part in cling film as a separating agent, the tape it down with duct tape in 2 layers to get a cast. He's then cutting it just as you would a masking tape design on a standard last, before removing excess clingfilm and transferring it to make a pattern the same way.
The thought might be to build up foam on top of the duct-tape pattern and make a new pattern from that, allowing plenty of extra on the seams, to be trimmed to shape on the model. This is where lasting helps, you can stab and cut without harm!
An even easier one comes to mind though - get the customer to wear three or more pairs of really thick socks before "casting"!