I put an AR 6-position collapsible butt stock on my SU-16, and it had a nice attachment point for a sling just below the butt plate, but there was no sling stud on the bi-pod forend. I tied a piece of black nylon paratrooper cord into a small circle and made a girth hitch around the barrel just in front of the forend. From an accuracy perspective, that's far from ideal, but it does allow a sling attachment point. I've used the girth hitch loop method to secure the sling on my Mossberg 590 12 gauge when it was so equipped.
I moved the Charlie stock from the SU-16C when I made it an SU-16E, and the Charlie stock is now on my SU-22C which I bought as an SU-22CA. The SU-22C still has the polymer forend that Kel-Tec supplied as original equipment, so I'll probably put a girth hitch loop through a pair of vent holes in the forend, although it's not a free floating forend so a sling pulling on the forend will pull on the barrel, but it probably won't be quite as bad.
The question for me is where I'll attach the sling to the folding Charlie butt stock. There's no way for me to figure that out until I have the sling in hand and I can start playing with it. I'll probably try several options before I find the one that works best for me. I have an ongoing thread in the SU-22 forum, and I'll post what works best for me in that thread that documents all the fun I'm having modifying my SU-22.
I'm thinking of getting the black Claw sling from Quake Industries. It's a little heavy for the lightweight SU-22C survival rifle I'm trying to create, but any good sling is almost as heavy and I don't want a light but not very useful cheap nylon sling.
Called Kel-tec and they let me know that there is a special 6$ attachment stud for use with the compact forend. Yes, it could have been a bit clearer on the website, but hey, the sling system is pretty well designed. no complaints.