If you want less sharp, just use a less optimum pinhole. I've only made a couple of pinhole cameras, but I noticed that my home-made pinhole (pop can, needle and sandpaper to make pinhole) was much less sharp than a laser cut pinhole with approximately the same pinhole size. You could also use a larger or smaller pinhole.
Thicker material (for the pinhole) will give more vignette, too, as the off-center points will receive much less light. Might get some of those weird reflection and/or diffraction flare effects too.