I own a glass shop so maybe I can help with the idea of using glass to divide the cups. You can take a piece of cardboard or poster board and use it to make a pattern of the inside of the cup. Take it to a local glass shop and they can send the pattern too their supplier and get a tempered piece of glass made. The pattern would have to be almost perfect because tempered glass can not be sanded or cut after it is tempered. Another option would see if the shop could get a piece of pyrex glass cut to the pattern of the inside of the cup. The glass inside a fireplace door is called pyrex, and it should hold up to the heat of the plastic. Hope this helps.