Currently there is no good pure declarative “react-way” to use Transformer tool.
But you still can use it with some small manual requests to the Konva nodes.
And it will work just fine.
Idea: you need to create
Konva.Transformer node, and attach it into required node manually.
Instructions: click on shape to select it.
Currently that demo doesn’t hadle saving of new node’s props into the state. It will be your homework.