I do find the assmuption that I'm a "he" rather interesting!
Apologies that had more to do with brevity of response than anything. Aviation professionals can of course be of any gender.
The answer to your question is you can't. What you are experiencing might be an unforeseen impact of the use of CCAMS where flights are allocated codes for the whole flight and therefore the pressure to release the en-route code as soon as possible so it can be reused isn't as great as it once was. Have you asked the units around you why they aren't using their own codes?
One potential issue is that if the aircraft switches from the CCAMS code the current NATS systems and anybody using code callsign data provided by those systems may lose the code callsign conversion on that flight and revert to the Mode A code display only.