It might not be as different as you think!
I pumped for my daughter during work hours since I worked far from home and she nursed until she weaned at 3.5 yrs.
Basically, I would get up in the morning and pump before she woke up (or if she nursed first, I would nurse her on one side and pump the other.) I would nurse her after I pumped, since it's easier for a baby to get your milk to let down than a pump. She was never fussy and I never felt like I didn't have "enough" for her in the morning after pumping (but that was my "fullest" time of day too.
She would drink milk from the previous day and I would pump at work at least once. I usually pumped for just about my entire lunch break. I would pump with an electric pump in my car while I ate lunch brought from home. I would also pump on the weekends whenever I got a chance (after she was in bed, after a nursing session if I still felt some fullness, etc.)
I think, by this point, if you're only cutting out one nursing/pumping session each day, you aren't going to do much (if any) damage to your supply. It sounds like, though, that you have a schedule going at this point, which might be a problem for your body to adjust to. For example, if you don't pump OR nurse at 3, you are probably still going to be full because your body is used to having to provide some supply for 3!
Think creatively about how you can make it work to pump more often at work. Smokers get smoke breaks, remember!! If you're uncomfortable, leaky, and full of milk you are going to have problems. If the company is being a pain about it, go to HR. They are required by law to give you a certain amount of breaks. Even a 10-15 minute pumping session here and there is better than none!
Hang in there! (Oh and by the way, my daughter didnt sleep through the night until she was 4. :)
M.