Rotorrookie
SOPs for underslinging live people will vary depending on the job you want to do and what you are trying to achieve. It is such an uncommon task that I would expect anyone who does it to write their own set of SOPs based on that job/aircraft/equipment/acceptable risk.....amongst other factors. I don't think you'll find one set that covers all operations.
I used to use a "Billy Pugh" quite a bit to lift people off buildings. Easy to use directly onto the hook but I had to establish and train using strict SOPs for possible aircraft malfunctions.
Dangling people underneath helicopters is dodgy stuff. If this is something you are going to do, I would recommend you get professional instruction on the equipment and professional guidance with your SOPs.
Tam