That's cool. I'm not sure I'd attempt at making them from scratch. I think they'd stick out like a sore thumb from the onboard styles.
124 ... I've made a number of backing tracks (SMF) using the on-board styles, changing drum kits, bass instruments, accomp voices, tempos ... etc. on both the kn6000 and the Pa900 ... on the Pa900, I've also recorded a vocal backing as an mp3 and played/sung over that ...
I wouldn't try to make one from 'scratch' either - wouldn't know where to start