Gaining

To my knowledge, trying to redirect growth to certain parts of your body is normally out of your control.

I've heard of sitting frequently can cause mass to start to build up there, though I reckon you already do that enough as it is 😏. One thing possible is to build muscle in those areas you want to grow, which would make them more pronounced, at the cost of a harder gain and even potential weight loss. I've also heard of people losing weight only to regain weight again, but in different areas. I'm not sure how much they've lost to have such an effect however.

The only way that might be possible is that, if you consume a lot of dairy, you may gain more in “feminine” areas.

I did a heavy cream gain for about two months, a liter of heavy cream a day. And I got soft in my butt, hips, thighs and finally my chest.

Just as you cannot spot reduce, you cannot spot gain. You can build up the muscle there or get plastic surgery. However, there isn't a special diet to get a bigger lower half.

The solution to this particular problem is squats.

Good luck with that! The extra weight will make exercise harder since you will be moving more weight, so start with a small amount of sets and reps and make sure to take ample rest. Besides that, your gut will be especially problematic since it'll ruin your balance on, for example, squats. Glute bridge and hip extension may be good beginning workouts, though just keep in mind not to get yourself stuck on the ground lol. Try to do something like 8-10 reps for 3 sets, though you may want to do something like 5 reps. You'll figure it out. Don't forget to chug protein shakes afterwards!

I've been noticing fat cavitation devices starting to become cheap enough to beat liposuction for DIY body sculpting. It's also easy to test too, someone used it on a pork belly and the fat layer nearly vanished.

Theoretically, if you can subtract fat cells in certain areas but gain all over, you can eventually force an hourglass shape by just subtracting the midsection, arms, and double chin/face. I got one ordered, but it'll take a week for it to arrive.