I have used the following rig with success. 1/8' dia. prestretched braided line is best but other small diameter line will suffice. Tie about 15" of the line to the sail grommet with a bowline snug to the grommet. Then feed the free end through the plastic eye at the end of the spar, back through the grommet, adjust tension to taste and secure by tieing half hitches around the doubled over lines. This rig seems to work fine. For the luff of the sail (the leading edge) I set up the outhaul line rather slack and then fine tune with the Cunningham adjustment at the tack of the sail (the intersectioin of the gaff and boom.) For the boom, I used a class legal adjustable outhaul back to a cleat on the side of the boom.
I'm trying to do this now with an intensity sail and both of those links are dead. I think I can follow Alan's instructions, but for the clew do I tie to both spars? Does it matter? and how much slack on the luff? I'm planning on having an outhaul and cunningham, but id still like an initial guess because "The tension on the head is absolutely critical." This description is given on a site: "Tie about 18" of low stretch line to the head of the sail and lead it through the eye on the end cap. Lift the top end of the gaff off the floor. Tension the luff until it draws up to form a nice smooth curve with the luff hanging just under the gaff." But pictures on these things would help a lot.