The real worry with bottle feeding for a whole day if BF, is that they develop a bottle preference and you have a full on nursing strike when you get back (or fussy behaviour)
Saying that, DD had expressed BM all through the night at 3 weeks and we were fine (although also had the above)
I found it really depended on who was doing the feeding, DH or a experienced FF feeder like my mum. There are some links here and here with techniques and tips for bottle feeding BF babies.
I'd say if it had to be done, then it can be, just be aware of potential consequences. At that age, there more likely to prefer the bottle if they used to the immediacy of it rather than nipple confusion.
Also be aware that you may completely change your mind about leaving baby for a whole day once it's here and in the first 6 weeks you're still coming to grips with BF and may not feel you've cracked it just yet. It takes a few weeks for baby to remember how to latch on for a feed.
If you go and leave baby, you will def. need to express. However you won't need to worry about supply if you are otherwise fine. Express enough to get comfortable (at least 3 times in the day prob) and trust that LO will sort out supply when you get back. They survive growth spurts they'll survive a one day dip in supply.
When you go to work, can someone not bring the baby into you, at least for one or two feeds?
It is hard and I had to work 1/2days a week after the first month so understand that there are times it has to be done.
If it is important that they take a bottle many of find that introducing one feed of around 3oz once/every other day around 3-4 weeks good. Since I returned to work full time at 4 months this is what we did.
Also finally, don't compare volume of feeds to FF babies as they are completely different. BF babies work up to ~25oz a day at around 6 weeks and then stay there (as milk changes over time). I remember getting very alarmed looking at how much FF babies took. Look on the pumping moms sections of kellymom for more advice on that and milk storage.
That was a bit of an essay
but hope it helps (and ignore typos of missing words as I never preview)