With more 4 bar endings, in RealBand you set the song length to the first ending,
generate the tracks,
now set the song length to the next ending,
now you can highlight the bars from the last 2 bars or whatever beat of the first ending to the last bar, then generate.
If you had an easy way to do this in Biab would be good, as I said once they get more tracks and bar to bar re-generate this will help.