After rather trivially messing around with animtools i came up with a really shoddy position where she (futa) can masturbate. If anyone with a little more skill can tweek this to be a proper job, it might actually be quite succesful. Please take a look and adapt it ( to line up the animation properly - reduce the size of the guy's penis so that it is not visible behind the "female" model. Then Drag the mouse until she is holding her own penis and it should be working.