it was on youtube, i dont know about you but i dont document every video i watch, so he has probably lost the link.
to answer the question, put a little circle of masking tape over the input hole, and two small rectangles over the + and - pads, then simply use car spray paint (make sure it says that it doesnt errode plastics), it will take about 3 seconds to do the whole thing and about 2 mins to dry, easiest way i know of.