There isn't any way to make the hair grow bushier but you can make them appear denser with make-up...
Yeah I know, I know, guys + make-up = no but no-one will be able to tell!
Just go to the beauty section of a department store and buy an eyeshadow that roughly matches your eyebrow color (slightly darker is better)
Then you just take a small soft brush and put a little of the eyeshadow on your eyebrows.
The eyeshadow will coat the hairs making them appear thicker and bushier ;)
Don't use any liquid products like mascara or eyeliner because they will make the hairs clump together and it will be obvious that you are wearing make -up :p