Wasn't sure if this was relevant, as the 'process' is pretty nil, but figured I'd put it out there and can delete if preferred.
from a game called Princess Maker 2. The ages are a little uncomfortable at the low end imo but its fairly solid AP, and you can take certain actions that increase the characters bust, resulting in natural growth over the course of a playthrough.
attached some images, some of them are when she is 'overweight' (scary-high expectations on that one) but attached anyway.