Simple answer is to use less calories while also increasing intake; calories in, calories out. Lower the steps you take, move a little slower, find alternative ways to do things that reduce your activity, and if necessary, keep a snack on you if you do have to move.

Of course you can only eat so much. Generally, fullness is caused by capacity limits and hormones. The former, I think, can't really be controlled, even with "training", at least for the long term. The latter can be worked around by eating fast.

Digestion is important too. Eating more protein has been proven to make people gain less, because they feel no need to eat more. Fiber and protein will slow your gain since you won't feel like eating. Stick to easily digestible carbs and fats.

I've heard experiences that people that eat as often as possible tend to also grow larger, more impeding appetites.

And of course, gainer shakes, ice cream, lots of snacks, heavy cream, soda

Have fun!

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!

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.