Are you using an adaptor seat to go on the big toilet? For my DS that seemed to help the most. He has an Elmo potty chair and the seat actually comes off and fits onto a regular toilet seat. Once he mastered using the big toilet with that seat on it we purchased the Kohler Transitions seat and replaced the regular toilet seat with it. It looks like a regular toilet seat, but has a middle layer that is smaller for kids. I'm probably not explaining this right so here is the link.
Also, what seems to help now is that DS can get onto the toilet by himself. We placed a small step stool on the side of the toilet and he has mastered climbing on. We still need to help him take off his pants and underwear because he is so slow at that part that he will sometimes wet while he is trying to get everything off. In due time :)
Yay for pooping on the potty! Thats crazy that your daycare won't use any seat adaptors. My DS goes part-time to a program and they let us bring in an adaptor and that really did help. I so so so appreciate your goal of getting DS full PT before the new baby arrives. My DS is 28 months old, but his sister is only 14 months younger and having 2 in diapers has been insane. I told my DH that those who have stock in Target are going to see a drastic drop in their dividends once both our kids are out of diapers LOL! I really can't believe how much we have spent on diapers over the last year :p