I once saw a way to air prune with natural things found on your own property. It was in a free book. Let me see if I can find it....
Ah! It was page 63 in Volume 3 of the
Farmer's Handbooks (these are seriously awesome resource
books detailing the nitty-gritty techniques of organic an
permaculture gardening. And they're free! And aimed toward beginners, with lots of pictures.)
The books are free to download. They have lots of pictures of setting up a air pruning nursery. Basically, they make a "table" with legs of sticks/bamboo, and the table surface of
straw and sticks. Then put a 6inch tall "walls"/frame around the edge of the table surface, and then fill that with soil. The pictures really explain it better than words do!