The Underworks 997 helps slightly; it goes over your hips so it smoothes out your profile somewhat. Also, T will probably help somewhat when you go on it, because it'll change your weight distribution. They've also started selling Spanx for Men in the UK, which will have the added advantage of being men's undergarments so you don't have to go to the lingerie section to buy them.

But realistically? The only real, long-term solution is diet & exercise. I had a pretty large posterior myself a couple of years ago. I put on a lot of weight after having the kids and my dysphoria got much worse because of it. So I started to watch what I was eating (chocolate is my Kryptonite) and I hit the gym.
OK, I'm still overweight now, but I was borderline obese back in 2009 and I'm now just a bit overweight. My weight is now at a level where the Underworks does a good job, and I've worked my way from a size 42 jean to a size 32 (in case any American readers think this means I'm still the size of a small country, those are UK sizes).
Oh, and Devlyn? Priceless!