Guys please hear me: DO NOT GLUE YOUR AIR BAG COVERS. EVER.
I did it on my calais I had the same problem, I took the dash out and put a stato dash in - this is the only fix. Unless you can find an air bag cover in good condition which matches your dash colour and the chances of that are slim. If there is a safe way to glue the air bag cover you must TAKE IT OUT first and be CERTAIN that the glue has set before replacing it. By that point you'd be better off putting in another air bag cover or dash.
Can't stress this enough DONT GLUE IT DOWN. It's just not worth having it not deploy when you have your girlfriend or mate in the car and you being liable/responsible for their possible injury or death.
Happy to help anyone wanting to tackle it and get the dash out to replace it or install the stato dash. I just finished doing it in my calais and was well worth it. You should be able to do it in 6-8 hours in and out.
Not sure if the cops would get you on it, but I found there were a lot of differing opinions. Most places had no idea what they were on about and just said they wouldn't pass it (RWC), Holden dealers said it would affect how it deploys, other holden dealers said it wouldn't affect it. An air bag specialist said it was purely cosmetic and wouldn't affect it deploying.
That was good enough for me to leave it for a few months but I stupidly glued it down anyway, thank God it's out of the car now.