We had some poop drama with DD, too. Things we did that seemed to help with the motivation:
1. She puts on character undies in the morning but if she has an accident she has to change into plain white ones for the rest of the day. If it's a poop accident, the undies get thrown away altogether. (I stole this idea from a potty training book).
2. She picked out a nightgown she wanted and she gets to wear it only if she has been accident-free all day.
3. She gets one M&M for trying, 2 for pee, 3 for poop.
It took her a couple of weeks but she kind of has it now. Just last night she went straight to the potty and pooped like it was no big deal, which was huge. In the past she would strain and try to hold it and carry on for a long time, eventually ending in an accident. I think having a few successful poops in the potty made it less freaky for her, so hang in there. I think a lot of it is just time and practice.