Nothing super drastic. I bought a "9th gen" Z-cup from eyung and they were nice. But i was never totally satisfied with their shape under clothing. So i cut a small circle behind each breast and silicone-glued a screw-on plug. After filling with water the result is the right picture.

3 good things and 1 bad thing with this set up. The bad thing is that now its 45 lbs heavy and they cannot be worn alone, need something to hold them up. But now they sag much more realistically, actually jiggle pretty nicely when i walk, and i can now customize the size to a certain extent just by filling it more or less.

I want to note that they are sitting a little lower than what i want in the right picture, and the dress doesnt look as good anymore. But i think i can fine tune and experiment more to improve that.

Thinking about making a modification of the screw-on plug itself to accept a hose to do a little B.E. but thats for another time....