Did you ever try moving to a smaller tub or changing substrate? I think if you moved to a 6 quart tub (can be found at the dollar store!) you might get some feeding response. Pack the tiny tub with crumpled up news paper or fake plants. put a towel or something over the tub to keep it nice and dark.

I would avoid assist feeding. You are feeding in the home enclosure right? Have you contacted the breeder at all?