If anything, I think it helps to get a little underweight. Limit your calories, and exercise vigorously ramping up to an hour a day six days a week, with a mix of cardio (mostly cardio) and resistance training to keep your metabolism up.
At the very least, do this before you have surgery. Before HRT if you can -- it'll make your hormones that much more effective.
As for weight gain after all is said and done, it's not going to be a panacea. If you've got a beer belly now, that's what you'll get going forward. It won't all go to your hips.