oh i wish there was a way to change it!!!
the best i have come up with is that there are some foods that make my lo poop easier than others, so i try to give them to him earlier in the day so he poops before bedtime! :lol:
since your lo is likely not on solids yet, you may just have to wait him out. if you are bf, maybe something in your diet will help, though i have no idea what!
i would wait to go to him till he cries, then treat it like a nightwaking. change his diaper & put him back to bed. no lights, no talking, no eye contact. do pat/shh or pu/pd or whatever until he is asleep or it is the wake up time you want.
sorry that's not much help, but that's all i've got!