Keep running shoes in the office and bring a fresh pair of gym clothes in every day. Before lunch go for a jog. After the jog do some lunges or push ups, switch it up each day. When you get back to the office go to the bathroom and run your head under the sink, strip down, wash yourself off with a bunch of baby wipes and spray your whole body with deodorant. Basically, a whores bath. After getting your work clothes back on go to your desk and eat your lunch which consists of a salad (no fatty dressings), some nuts and a serving of fruit. At this point the only liquid that exists to you is water, after a jog you will learn to love it more than anything else. Try slamming a Dew after a big run and see what your body thinks about that horse piss.
Instead of taking that long of a "lunch" break, eat a healthy lunch at your desk and leave work early to have time for the gym. If either of those options don't work, you need to find a new job that can accommodate some gym time in your life. No matter what you do though you have to start eating healthy ALWAYS, especially if you can't find the time for exercise. If you eat garbage and work out you will still look like garbage, you'd be amazed at how few of calories you burn when working out and how much there is in the food we shovel into our face.
Your body evolved to chase prey over long distances on foot; to fight, to walk around all day scavenging; to eat meat occasionally, and to go days without food. The way you're living your life doesn't even come close to that level of excursion or occasional starvation. So to make up for it you have to run like a bat out of hell 1 hr a day and eat like a rabbit, that's the tradeoff. I know it sucks, but it's what us cubicle people have to do to attempt to restore balance to our body. Needless to say the best job choice I ever made was finding one with a gym in the same building.