I'm starting too with DD nearly 2.5. I have three big containers of treats- trying, wees, and poos. If she tries she gets a little choc button or something similar. A wee gets a freddo or similar. A poo gets a kinder surprise or giant freddo.
Pretty sure no parenting expert would support this plan but you know what? It's working. She's started asking to go and nearly giving herself hemaroids trying to push a poo out that's not there .
I also found leaving the nappy off helped with no undies either, I think she didn't know the difference.