The Playable RealTracks should be working on Drums but they haven't got them enabled yet.
If you load Sforzando into a Utility track and choose a PG Drum Kit,
you can then select Piano Roll, select a Utility track, drag n drop a midi drum solo into it setting the bars in to position the midi.
Go into the Audio Edit for the RealDrum track and mute those bars that have midi. Adjust the volume of the midi drums to match the RealDrums.

Videos: BB22-Drum-Solo.mp4
BB22-Drum-Solo2.mp4

MidiSolo to try DrumSolo.mid
You can use DRUMSOLJ.STY and Force Midi Drums as Jim suggested, you can generate up a midi drum solo track in another instance of Biab then just highlight bars on the Chord Sheet you like, now drag the Drum track at the top of BB to the MID Drop, when green drag and drop into the other instance of Biab choose the track and position.
Also in the Midi Import dialog select Merge so it won't erase any other solos you dropped in.

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