Odd question about penis mods

[paraceta]

I been trying to find a way to have a sim with penis only during sex and hidden when not. Been searching fora few days but what should been a easy find has turned in to a 

labyrinth of bad google results.

 

Sorry the name for some reason escapes me, the sim i want to change is the spellcaster that is the mischief spell trainer,  he has no genitalia as far as i can remember, so i thought it would been cool if he had one selectivly during sex lol