Well, to make a long story short, you'll need to remove the lens, bollix the shutter so it stays open while you hold the button and/or add a cable release adapter, and disable any light meter based lockout for low light.

Honestly, I'd suggest keeping that one original and converting something easier, if it's your first pinhole build. You only have one emulsion choice in 126 film; if you convert a 120 camera, you can get dozens of emulsions in B&W, color, and trannie, plus have a negative anywhere from 5 to 10 times the size of the 126 frame.