Another thing to remember is that Chameleon are 'stimulated' to eat by the 'sudden appearance' of a prey item.
It's like a hungry lion is stimulated to chase a gazelle after seeing one run by.
So, do not leave the cup with the moving food in the enclosure too long. To your chameleon, the cup with the food will just become part of it's envirmonet and will quickly learn to ignore it. Leave the food cup with the prey in there no longer than an hour or two, then take it out and try again later.
The sudden appearance of the roach, cricket, superworm, etc is what stimulates 'an attack' from a chameleon in the wild, and can work the same in captivity.