I've discovered via trial-and-error methods that if I create a basic 3,4,5 or 6 note chord in the BIAB notation editor, then open the "Piano Roll" window, I can improve the pseudo-arpeggio by slightly varying the STARTING point of each note, where by default all the notes in a chord created via notation have the exact same starting point.

It "feels" like there could be some way to create such "strums" without the piano roll editor, but so far nothing appears to support such a "feeling"!

Fortunately, this song only has a few bars where the strum is required...so off I go.