That was my thought, too! Maybe use the flat circles and include some different sized small round ones, too, to give it more dimension?
Get them on the cake then get the CK Gold Highlighter going through your airbrush.
PS I'm the one who posted the question about edible gold sequins (gelatin) awhile back. I watched the tutorial and they came out AMAZING, but definitely not the look you're going for.
And be sure and tell your customer that part of the cake is not edible and not even non toxic.