I did the same thing a few months ago and you really dont have to be too fine with it. I didnt have a needle or anything so tried painting it in with a fine paintbrush and got the nail polish all over the knob lol the numbers are recessed so all you have to do is get a rag with nail polish remover and wipe the mess up and the numbers still have the polish in it and it looks great even months later without redoing it. cheapest mod ive done and looks awesome with all of the red accents to the car like the red stitching in the leather seats.
even easier is to use one of those shiny/glitter pens. You can get like 6 for a dollar and because its a pen with a fine tip, it fits right into the groove and you don't have to worry about having steady hands. I used silver for mine (on the ex)
Just did this yesterday. My wife didn't have a good nail polish color, so I bought some for 99 cents. Blobbed it on nice and thick, let it dry for 30 minutes, then wiped up the excess with nail polish remover and a cotton ball. Looks great and didn't take more than 2 or 3 minutes.