Thomas the Train and potty training

I've been pushing through with potty training Aden even though it has been very hard.  Our good neighbors have this Thomas the Train that rides around on the track that I bribed Aden with if he could poop in the potty.  He did, once.  He hasn't since!  So, shout out to the mom's out there.  He has the peeing figured out, but that is it.  What do I do?!

Kate loved riding it too.  But sadly, it hasn't been out since!