I did this with my top zip long pocket in my highcamp, the KU 3 bar sliders on my long pocket are 3/4" the common loops on the highcamp for the chamber pocket is 1", it would slip out once in a while. I got my longpocket when the KU packs where still in production, the KU pockets might come with both size 3 bar sliders now so it may work better. Currently I'm using my KU longpocket as a stuff sack for my BCS2. I can attach it to the outside of my pack if I need to. For whatever reason the 3/4" 3 bar slider stays better when attached to the webbing loops on the outside of the pack rwhen it's moderately full.
I used a small piece of duct tape to keep the small 3 bar sliders from coming out of the larger common loops.