Sgtar15, I feel your pain, literally. My back isn't nearly as bad as yours but in going to PT I have spoken with a number of people that have had the same procedure and they are doing pretty good. With a lot of hard work you should be able to get to a workable level.
One thing they have me working with is a Bodyblade. Look it up at Bodyblade.com. It's designed to strengthen the torso, strengthening the underlying muscles you normally don't target directly when working the abs. I picked one up on Ebay for $60.
Another torso builder is using a Physioball. Those big rubber balls that you always see women working out with and you think what the hell is that going to do for me? I'm too macho to use that. Again, it does a great job and is very low impact on the spine itself. You are basically doing crunches or lying on your back rolling the ball with your feet forward and back, both feet on the ball at the same time to concentrate on the lower abs, keeping them tight. I'm sure you have heard the term "puck and tuck" at PT. Keeping your abs tight at all times.
There are also a number of spine stabalization exercises I have been doing. I could send them to you if you would like.
I went from not being able to walk over the Christmas holidays because the pain was so intense to now I can play golf, run, bike ride, do anything I want by doing these exercises 3 times a week. My wife tells me I have developed a mini 6-pack. Gotta keep going, she loves it.
I think the only thing that really still bothers me is, just like you, sitting for a long time. Airplanes or meetings are killers. Just get up as often as possible to move around.
Oh I also forgot, if you carry your wallet in your back pocket, take it out. Done wonders for me. A walletecktomy my Dr. calls it.