Quite simple really. Just get your soldering iron good and hot. Just stab it straight into the stock where you want the texture to be. It's simply a bunch of little dots. Try to be somewhat random in your application of the dots - if applied too uniformly/systematically I don't think it looks as nice.
If you are concerned about how it is going to work, take off the recoil pad and try doing it inside the stock where it won't be seen first. You'll get the hang of it quickly.