If you are worried about him eating the substrate, I would say either a) put him on paper towels or b) get a largeish paper plate and feed on that. I have planter drip catchers for hides, so when I feed i usually flip over the cool side hide and put the heated up rat down on that. When he comes to investigate, I give it a little prod or shake with the tongs and once he strikes, I close the lid of the tub and tun off the lights and leave him alone. When snakes eat, they are very vulnerable, they are out in the open and they cant go anywhere fast. If its is bright and there are giants (you and your family) hovering he might not feel comfortable swallowing. Next time you try once he strikes, just close the lid, cover the viv and leave him alone. Once he is a bit more established, there will be plenty of time to watch him eat. It usually takes my guy about 20 minutes from the time he strikes to start swallowing, so be way patient, and resist the urge to check on him.