hi there isaac:
you could probably do it pretty easily, and even have a way to use different lenses if you wanted to. you'd probably want to figure out the hyperfocal distance ( http://www.mountainstorm.com/HyperFocal/HyperFocal.html ) so you can have a pretty good handle on dof, you wouln't need a ground glass, just make a "V" ( back corners to middle of top ) that would be your sight, until you make a sports finder or aux viewfinder type thing. if you don't have any cardboard or matboard, you could make it out of basswood, or cheep plywood ( hobbystore type ) and glue them in a moulding. instead of bellows you could make it a box inside of a box, and have it marked where the different focal lenght's would be, and have it lock into place. my brother built me a 8x10 pinhole kind of like that ...