I have applied glitter mixed with the top coat of D2T or Solarex most of the time. The only other way I have applied it is to shoot the Createx medium like Illustration Base to an area that I wanted glitter then sprinkle the glitter over the area. That way if I only wanted some red glitter on the red down the sides and/or on the cheek of a rainbow trout, I could spray only that area lightly with createx and then sprinkle red glitter lightly over that and it will only stick where it is wet with the createx.
If you are going to try and spray the glitter with your airbrush. Keep in mind that if your are using an airbrush with a 0.5 nozzle, you don't have an opening of 0.5 unless you have the needle pulled all the way back. With a 2 stage airbrush, down with the trigger for air then rock the trigger back to feed the medium. You are going to have to rock the trigger all the way back to have a 0.5 orifice. If the needle is in the nozzle at all, you have a 0.25 opening or less. Hope that reads ok.