• Paste (Mix) - This will mix the audio from the clipboard with the existing audio instead of overwriting it. You will be given the option to set the percentage of the existing audio to keep and the pasted audio to mix in.

This will paste between instances, so you can have another instance of BB running with a realdrum track file loaded into the audio track with all the drum shots at the end then copy and merge these hits into the realdrum track of your song that has been moved to the audio track.
This way you can create up your realdrum track just how you want it.