Isn't there a bar offset setting in FL ?
You don't need to know how to use Reaper to drop audio or midi clips into it's tracks, you may have to click the FX button on the track to add a vst that's about it, you had to ask how to do it in Biab because it's not well thought out and designed to be a no brainer.
Just look at Reaper as extra tracks with super easy drag n drop audio/midi with non destructive editing, you don't need to know anything else.
You can even inject the Biab source files directly into Reaper without creating any wav files.
I tried to get PG to make a small vst like FL studio has to sync it to any DAW, so Biab will follow the DAW transport.