the Sacred Harpies around here have been doing this ever since I can remember...I thought everyone knew it...don't know whether it is 'standard' but they also do a 'refrain' of the last line with a 'prepratory call' by the leader to begin the refrain...thus...

All who now as foes combine.
Babel's garments we've rejected,
And our fellowship is o'er,
Babylon is fallen to rise no more.
....Baaaaaa....(drawn out...with the rest following a half beat later
Babylon is fallen, fallen, fallen
Babylon is fallen, to rise no more.

Hope that is clear enough...it is obvious when you hear it once...