The smaller ducks are not wanting to accept the newest baby duckling; two of them started pecking at the poor thing. Its so sad, because it is all alone in its incubator now(with a small cup of water and a small cup of food.. I had today off from work and so I brought the duckling out of its incubator a couple of times and rubbed its breast with my thumb. It seems to like that btw. But I can't guarantee I will have tomorrow or the next day off, so I don't know what to do.
Even if there's only one other duckling that accepts the newbie I would put them together so it's not alone.

My hard-headed motto, honestly, is to keep trying stuff until something works... I do feel like this a lot though!
Jolenesdad’s suggestion is a good one as well, to try an individual duckling who will get desperate enough to accept companionship from this mini invader!!!