I know this will not make a difference to the vast quantity of empty bulbs, but I have just converted one into a mini BB store, a bit more pocket-able than the 500 size bottles they come in.
All I did was drill out the pierced end to about 5mm, cleared out the swarf and found a suitable cap in my magic box-of-bits. I did a weight for full vs empty and reckon there is about 170 BB's in there.
I might increase the hole size a bit, they seem to 'log-jam' occasionally and need a quick shake, but otherwise I am well pleased with my ten minutes effort in the shed. My next prototype will be for pellets, but gut feel is there will be a lot more jamming...

Happy tinkering.