Jo, did you ever try the newspaper trick? I don't see it here very often so I don't know if a lot of people know about it, so forgive me if this is something you already tried. After about 2 or 3 refusals of live hoppers I like to stuff the babies shoeboxes full of wadded up balls of newspaper. Put enough in there so that it's completely filled. Then give the snakes a few days to make tunnels through the paper. Release a live hopper or two in there for a day or so. It really seems to help the timid ones a lot. I think it gives them more opportunity to hunt from an ambush position.
Mark