My pinhole is built around a 5x7 picture frame that serves as the "film holder". I put in a piece of paper, it's held flat against the glass of the frame facing the pinhole. Close the back, expose the paper negative, develop, let it dry. I keep an 8x10 sheet of glass (decent quality anti-reflective framing glass) next to the enlarger. Once the neg is more or less dry, I just lay down a fresh 5x7 sheet on the easel (only because I'm too lazy to move it), lay the negative on it face-down, lay the 8x10 glass over both for some degree of flatness, and expose (without a lens in the enlarger, for the reasons stated above). Then, another round of dev for the newly-minted positive, and there it is.
Not counting the drying time, it takes me a total of under ten minutes effort to go from an exposed sheet of paper in the back of my pinhole to having a contact-printed positive. A significant chunk of that is spent determining the correct exposure time for any given negative (not very good at judging them yet-usually takes me two or three tries).
I could improve the quality, probably, with a proper contact-printing rig. It would hold things flatter and in better contact than a relatively lightweight sheet of glass like I'm using now. But, so far it hasn't been enough to worry me, since we're talking about pinhole here anyway. Crisp isn't exactly the point.