It is almost silly how easy doing some moderate BE is using a base WAN model. You have to use the word "inflate", not grow or swell. For instance, the prompt for this one is:
2girls, 2 gorgeous beautiful cute women in a gym locker room wearing flimsy thin sports bras and panties. The white woman on the right has black hair, brown eyes, small breasts, and a round butt. The woman on the right has straight blonde hair, blue eyes, small breasts, and a gigantic butt. They both look at the camera and smile, then their breasts very slowly inflate to (((gigantic breasts))).
I did use 1 LoRA, the breast slider set to 0.75 so "small" breasts are actually DDD-G range. It also boosts the amount of growth you get when you "inflate" breasts.
ŠPunchy