I understand your idea, but i also see a different approach.
The way you like to build your B&B-line is in one long continuous row -right?
What you could do with that design, was to think about one 'segment' -perhaps 4 bar(?) -as one BB-line
Then your long continuous BB-line would be made out of segments of 4-bar each, and be represented in song-editor as a stair-case like pattern.
What do think about that idea?
One benefit that design would have, would be a possibility to use BB-line8 in both 8.-position but also f.i. in position 32. -or 34 -or...