Get the nipple as hard as possible. This is very important. It will prevent the nipple from being noticeable later.
With a Qtip or brush apply Prosaide or similar professional grade adhesive to the nipple and surrounding area.
Invert the cover and using the tip of your finger place on to the nipple in the centre of the cover.
Press down so the erect nipple is pressed all the way down and then press into the surrounding glue.
Using a Qtip, carefully apply glue under the edges all the way around and let the foam fall down against it.
Using the Qtip dipped in glue carefully blend outwards across the edge to seal it against the skin.
Coat the entire surface of the cover with glue, dry and powder.
With a Qtip dipped in rubbing alcohol (91%-99% preferred) work out any wrinkles or folded over edges that may have occurred.
Dry the alcohol and powder.
Your cover is now applied and ready to paint.
Strong glue is used. DO NOT just peel the cover of. Be sure to use plenty of skin safe adhesive remover. Let the foam swell up and gently work the cover off with cotton pads or removal brush dipped in remover.