Hey Mike,
If you're comfortable doing so, I'd go ahead and give him something to eat (ie. force-feeding). If you're not comfortable, I'd just separate them and keep trying for another week, but force-feeding should be on your mind. Send me a PM if you need any more help than has been described in the articles section (
http://www.thamnophis.com/caresheets...=Force_Feeding).
Definitely have a look at the underside (ventral side) of the snake to see if it is convex. If it is underweight, it's time to act. Personally, I'd force-feed something small that has been given a vitamin supplement... even a drop of vitamin into the mouth of a dead fish will suffice.
Rick