Hi Tom,
maybe you could edit the existing drum styles to get what you want by finding one that's close to it. Existing drum styles can actually be edited in the keyboard ( including in steptime), whereas the other parts of the style ( bass, etc , have to be re- recorded from scratch. You also have the option of style assembly editing where you can mix n 'match style parts from the various styles onboard.

Documentation on creating styles is far from great, but it can be done.

best wishes
Rikki