Cleft grafting, as I understand it, involves Removing a wedge from the top of the stump, a saw will make life easier, making the remaining gap as thin as possible while still allowing the scion to fit into it, insert the scion, lining up the cambium layers, use polythene tape (strips of carrier bag work aswell) to completely seal the graft from the elements.
A Picture:
http://generalhorticulture.tamu.edu/...paga/p92f8.gif
Preparing the scion: the chosen material to be grafted are cut down to size, about 5-10inches, making a sloping cut above a node on the top sloping away from the bud, and a flat cut on the bottom.
Using a razor sharp knife the bottom of the material is cut at a slope on both sides to get the end to tapir into a point. Making the cuts about 1 inch long on both sides. Don't touch the exposed cambium on the scion or on the stump.
Hope this is of some help, another idea might be wedge grafting, I can tell you about this as well, or do a Google.
-Matt-