Like you, i work fewer but longer days each week. Make time on your days off to pump, even once per day. This will help keep your supply up, and it will also allow you to stockpile extra so if you're a few ounces short pumping on a work day it won't be a problem. Also maybe if you cant take enough formal breaks at work, you could bring a manual pump as well as your electric pump and take a few quicky 5 minute breaks with the manual pump, and a few real breaks with the electric pump.
j