A one inch diameter bar of lead about 4 inches long will weigh about a pound.
Get your calipers and measure the width of the stock at several places
Go and find you some lead, an old skillet, a camp stove,some one inch ID aluminum or other metal tubing, and a brick. The inside diameter of the tubing has to be less than the width of the stock with some safety margin depending on how prone you are to screw things up.
Melt the lead down and pour into the the tubing and throw into the snow bank to cool.
Go into the garage and get your drill and put in a bit that is exactly the inside diameter of the tubing.
Put the stock in a vise of some kind and drill a hole or two. If you screw up and drill to the outside of the stock then grab up the brick and use it on your head a few times.
Cut the tubing into lengths that will fit into the holes and remove the tubing from the lead.
Using a yellow handle hammer pound the tubing into the holes. Other colored handles will cause the stock to split and then you will need to apply the brick again.
Once you have the lead in the stock go and get you a lag bolt and find a drill bit that matches it. Drill into the lead so you can anytime you wish put in the lag bolt and pull out the lead.
Put the recoil pad back on.
Vacuum up the floor before your wife gets home and use some Oxyclean to get up the blood that dripped from your head after you used the brick. Put some antibiotic on your head and a good bandage.
There are ways to calculate how much lead you need but it is somewhat beyond the needs of this thread.