Yeah, nice gun. I think if I was modding a gun like that in such a way, I would go all the way and install or modify something to secure the lever fairly strong in place. Maybe a pin with a spring action button? Or something like that.
Depending on your budget you can get a Custom Stock CS1000 FT stock. They sell on ebay and have a fitment for the Pro Sport. They are the only ones I know of who make a dedicated FT stock for the Pro Sport. This also gets you the adjustable cheek piece. You can sell your factory stock and recover some of the cost.