Knife them with a fine scalpel blade it's quite easy, use a gummed envelope (drop or two water and ant retouching dye needed) and a spotting brush to cover up the knife marks. It's far easier than it sounds. It was the standard technique for over a century. and it does work
This worked for me to prove the concept. Unfortunately I got a bit carried away spotting back. Scratch one dangerous treehouse. Good thing I made two.