BirchwoodCasey's Bore Scrubber Synthetic safe formula isn't supposed to harm synthetic stocks. But I think that it's primary that if you happen to get some on the stock it won't hurt it. I don't know that it's actually designed to use to clean the stock. If you try it, maybe first use just some on a clean cotton patch and rub on an area of the stock not easily seen.
Otherwise, I'd first check with the firearm manufacturer to describe what type of stain and what they recommend.