Maybe with some kundalini yoga, but you need to develop muscle, and fat IN THE RIGHT PLACE, and that can mostly be done with more of a workout.
You can achieve this by doing specific motions that straining your muscles. Since Kundalini Yoga is a Yoga of motions, it might help, but notice that it were not specifically created for this, and there are other physical exercises that are specifically created for this reason, which are more efficient in this area.
I noticed muscle development throughout my advancement even if I didn't worked specifically on them, but I think you should.
If you are slim, you should increase your protein, and calorie intake, with a good workout program that works on the parts you want to be thicker.
If you are fat you should not increase it, but rather make a healthy protein&vitamin rich diet. And do workout.
Weights are not needed. cardio is excellent.