JJ Licea was kind enough to take pictures on the steps to grafting a scion to an avocado seedling.
Cut toward the center at one side.
Do a matching cut at the other side of the stem towards the stem center.
Continue your cut until you can remove the top stem.
Split the middle further down to form the cleft. About half an inch further down.
Create your wedge like you normally would. Cut both sides, you can whittle away until the cuts will match the cleft.
Insert the wedge.
Wrap the graft union. Prewrapped the scion with a grafting tape starting from the top. See how it is perfectly aligned with no bulging at the union. It looks as good as whip and tongue but easier to do.
Reinforce with rubber band. Just scratch the rubber band by 50% more and wrap around the union.
Wrap the rubber band with grafting tape so that it won’t deteriorate quickly and you’re done.
Keep the grafted plant under a shade like a tree. If you don’t have a shady area, you can use a tomato cage and wrap it with a pillow case.
Ken Ueda showed here how to prepare your scion.