Certified GKH Gardening Expert
Potassium silicate can help here, although you will want to be careful not to overdo it. This can make the soil too alkaline, but it does wonders for the structure of a tree.
Another thing... Those supports only need to be used for about a week or two after transplant until recovery of the rootball. After this, the tree may begin to rely on the braces for support. This will cause the tree to have little to no support on its own.
Slowly loosen the braces over time, and the tree will strengthen up. If the tree snaps, it will regrow with no problem. Just don't use supports anymore than needed. This is only necessary to let the tree settle into its place.