...wear Captain epaulets if he's wearing FO epaulets, or if you could find them with 5 stripes all the better.
Don't really see much else you can do about it though other than not fly with him.
I like your thinking...
But the next step up from Captain is Rear Admiral which has one 2-inch stripe
Unless you know something about navy insignia, that just ain't gonna have the same effect.
Still, if you're handy with a needle and thread, you could come up with something with 5 stripes on your own.