Unfortunately @Badger there is no simple or easy way to fix this (on the BRZ atleast). I've looked into this abit and the options I came across were:
1. Smoothing the moustache, filling the holes and painting it. - The bodyshop I took it to said they could do it, but it'll look terrible and he'd rather not do it.
2. Buy a US spec bumper / facelift bumper - Expensive
3. Wrapping the moustache - Cheap, but the holes would still be noticable
4. Cutting the moustache out.
5. Getting a moustache cover (Kansai Service make one) - Best option I could fine.
6. Replacing the bumper with an aftermarket one.
There is a load of info here: https://www.ft86club.com/forums/showthread.php?t=4265