I 3d printed little containers that fit inside the grip etc, so you can make your own removable plugs without having to get a chunk of steel etc machined. I really should tidy up the STL and post it for other people to use.
This would be awesome, I love this idea. I was thinking of making some removeable weights but didn't think of 3d print. I would love to get your plans then I just need to find someone to print.