I cut out a flower and then placed the cup in the center and traced around it. When I cut the center out, I cut it just inside the line. It's hard to tell in the picture, you can see it better if you click to enlarge the picture. Then I slid the flower over the cup and taped it on.
The kids have been learning about the butterflies proboscis (tongue). Their tongue is like a straw and they use it to drink nectar from the flower, so that is what we did. I put nectar (apple juice) in the cup and they used their proboscis to drink it!