Hey Bob,

Wrong forum, this goes under recording forum. This one is for posting songs.

But to answer your question in brief: in a DAW like Sonar you will find programs such as Addictive Drums or Session Drummer that you can use to trigger and create as many drum fills as you want that will lay over top of any Real Track fills, and you can cut and paste to your heart's delight.

They sound pretty natural. It is very difficult, to me anyway, to cut and paste drum fills of the kind I think you are speaking of by splicing Real Tracks. You need a drum sampler inside your DAW to add the extra stuff is my short answer. But that is just the way I do it. Anyway, this needs to be moved to the recording forum.