Pumped while working FT for a year--
I don't think you can exactly replicate "on-demand" feeding when you're doing bottles at work and nursing at home, because the demand works differently. When a baby demands more from the breast, they get a slower stream of fatty hindmilk (then they get full)-- whereas when they demand more from a bottle, it just keeps coming and coming full stream, and they end up eating more than they would have eaten at the breast, potentially. I know you know all this! But not over-doing the bottles at work is really key for a lot of women so that there is the right balance of the baby wanting to nurse enough to keep your supply up.
I don't know how old your baby is, but once my baby was a few months old I made the bottles 3.5-4 oz always and sometimes he didn't finish one and it went back in the fridge for the next feeding (Dad watched him so he knew the breastfeeding storage rules). I'd leave 2-3 of these bottles and most days he only ate 2, but it was nice knowing the 3rd was there just in case. That way when I came home he was hungry for me and nursed all late afternoon/evening/night/morning. How much you leave will depend on your hours away. I was gone 7-8 hours. A breastfed baby at daycare will often eat and eat and eat and the DCP will ask for more and more milk and then baby doesn't want to nurse as much at home, then supply goes down and you can't keep up with the pumping demand.
Some GREAT articles to print for your DCP on kellymom.com in the pumping section!