It's probably hollow...
I thought about this hard when building a rifle for my 5 yr old boy.
I decided that it would be possible to chop the stock, then fill the butt end with epoxy. You would then be able to grind down the butt plate and mount it with screws into the dried epoxy.
In the end, I decided it would be easier to work with a wood stock, so I found a beater for $25, sanded it down and chopped it off to 10" LOP, refinished it and installed a flip-flop for the butt pad. With the refinished wood stock, the gun actually looks great. When my kids outgrow the stock, I'll just put the barreled action into a longer stock.