I have asked for this also, I suggested to them to allow bbw4 to open the chords from midi file dialog, then once it gets the chords it simply copies them to clipboard that is then pasted into the plugin.
I tried making a script to do this but was having problems accessing bbw4.
With this quick copy/paste either way with BBPlugin and Biab you don't need to save it to SGU
Biab > File > Import > Import chords from MIDI file..
Highlight all chords > ctrl C
BBPlugin > ctrl V

An AutoHotKey script can be made to do this:
Open Biab
Open Import chords from MIDI file..
Open browse window
Get Chords
Close dialog
Select all chords > Copy
Close Biab

Now you have the chords in your clipboard ready to paste into the BBPlugin.