I dont think there is an option for a pocket clip. Certainly AFAIK Streamlight dont offer one. I think you have two options, one is to rig up a clip yourself or get someone from CPF to make you one (if your lucky) or two buy a pouch with a sprung metal clip so you can use it without a belt.
Sorry but unless I'm mistaken you dont have that many choices.
i had my strion set up with one of those cell phone buttons that click into the belt clip holder. Ok that was about as clear as mud. Ya know the little tab with adheasive and the belt clip unit. Great little set up for lights like the strion.