Can’t be done. I suggest that you send a Feature Request to the AE Team -> https://www.adobe.com/go/wish
FWIW, I recently sent in a Feature Request asking for Range Selectors to be a part of the Repeater Shape Operator. This Range Selector will work analogously with the Text Tool’s Range Selector. I then asked for Opacity as well as Color to be part of the properties within the Repeater. This will then allow us to work effectively and creatively within the Repeater.
Cheers
RoRK
Intensive mocha & AE Training in Singapore and Other Dangerous Locations
Imagineer Systems (mocha) Certified Instructor
& Adobe After Effects CS6 ACE/ACI