The only fix is to install seats with them fitted - they were standard on sport seats (and hence sport models), so if you can find a pair from a scrapper, buy them, as long as the airbags are intact.
Even if the bags have been removed, you can still transplant your own into the new seats - there was only ever one type, although several colours obviously.
If you find a pair, I can always help you in the fitting.
Cheers,
Mike
PS, Did you get the correct tow ball holder?