Peter,
As answered above, I can't see any reason why you would do it differently than taking the front sling off. Yes remember several other Regiments in riot situations being shot.
I was trying to find the video of a Scots Regiment where the lad was being dragged out of the back of a Pig by the rifle in a riot, and the reason why not to make a loop from the rear part of the sling. Fim is better than words, if I locate it I'll put it up.
The woman was trying to cock the rifle as she and others pulled him, so thank God he followed SOP's on that day!!