There's a scene based on this concept in the first issue of my comic
The Cleavage Crusader:
http://members.expansionfan.com/The-...Crusader/c=57/
Its not a huge part of it, but I thought it might interest you all the same. #2 will have a similar sequence, but its a little more ambiguous as to whether it's the masturbation causing growth or the growth causing her to masturbate.