personally i wouldn't introduce new ferret members until after the breeding season, means hormones can settle down, but then castrating should speed things up a bit though i'm unsure by how much . .
feed wize try a beaten egg daily, it may be that he's too hot to eat a large meal, the egg will be a treat and give him protein, gives him something in his stomach, then try any scraps of meat, the turkey legs are good idea, i buy them for the dog from time to time, they cost approx £1.10 or there abouts
off cuts from butcher, sausage meat anything that could be really interesting to him as