Oh how I understand! I also sit at a desk all day. Here's what I have done to change my snacking habits.
I get to work at 7:30- I eat my breakfast at 8
At 9:30 I have a snack such as a sliced apple or a cup of fat free yogurt
At 11 I go for a 30 minute walk (this delays when I eat my lunch)
At 11:30 I eat a a light lunch, such as a sandwich or a bowl of soup
At 1 I have a bag of 100 cal microwave Kettlecorn
At 3 I have another snack such as baby carrots with hummus or celery sticks with salsa
At 4:30 I go for a run and then I head home.
As you can see I eat all day long. Hope this helps and maybe gives you an idea of how to tame the growling tummy tiger!