Do you have any LCD monitor wipes? If so, pull out the battery from your phone and use the monitor wipe on the ball. Hold the phone up in the air with the ball facing down so that any excess liquid from the wipe doesn't go into your phone. If the wipes you have are really wet (like to the point where you can ball it up, squeeze, and have it drip) then you might want to let it sit out for 30 seconds or so to dry before you use it.
It won't get you back to the factory look but it does a decent job.
