Unfortunately the ears on CASTs in this game for humanoid versions were purposely made to look speaker-like, the only thing that'll change a CAST's ears to another ear type are some types of face variants which only deviate the type of robotic ear for Male CASTs I believe depending on which varient, and the beast face variant which adds beast ears instead (this one probably isn't in NA yet). I think a good suggestion, or at least one I'd like to put out there, despite nothing like this existing on JP that I know of, would be to add face variants to CASTs that allow for regular human ears on top of the existing CAST ears.
This is an example of how face variants affects CAST ears in JP, for a male CAST at least; it'd be cool if they added human ears to the face variants, where it'd actually add ears to the CAST similar to how the Beast Face variant does:
