Skin codes
If australia goes down the compulsory Mode-S path, this can easily be achieved, as each transponder sends a descreet code.
In Europe I beleive mode-s is compulsory, or soon to be. Mode-S can also be used to transport traffic information for ADS-B, so I can feel a change to mode-s will be inevitable in the medium term.
This will give all aircraft a descreet transponder ID and should be easily integrated into TAATS.