Kellymom.com and La Leche League may have a little advice about being able to keep breast feeding even if you can't pump on a normal schedule. I found that I had to supliment with cows milk formula, even though I pumped regularly (every 2 hours) and breastfeed when we were together. Babies consume more from a bottle because it is easier, don't beat yourself up about it.
Some options would be:
Pump during your breaks (which may not be enough), and on your days off and evenings off breastfeed. Your body figures it out, I promise. I was away from my daughter 11 hours a day 4 days a week, and we breastfed exclusively the rest of the time. I could tell that my breasts carried more milk on my time off. I don't know how my body knew that it was my weekend and to produce more, but it did.
Supliment with donated breastmilk. I hear it is expensive, but would be better than cows milk formula. Do you attend LLL meetings? You should start going to a breastfeeding support group before you have the baby. There may be a mother there willing to donate her excess milk to you. Sounds weird, but so does drinking the milk from a cow.
While you are on maternity leave you could pump and get a small supply stashed, it would also help build your supply up. Invest in the best pump you can, remember that formula is very expensive. Think of it this way: you spend $700.00 on a decent pump and you only have to buy a can of formula a month. You spend $150.00 on an ok pump and you have to buy a can of formula a week. A great pump will pay for itself in about 6 months or so. Medela makes the best pumps in my opinion. If you are unsure as the kind you want, rent one for a while.