add easily a radius to a path

At the moment it's needed very much manual work to achieve a radius to a sharp edge. But it's not hard to programm some tool to get it faster. It can be done with these steps:
- mark a sharp edge
- click on an icon for the radius tool, it appears somewhat similiar to the scaling tool handler
- moving the handler does the following:
    add two new nodes straight to each connected node
    delete the selected node
    make at each new node at one side a bezier curve with 0.6 times the distance from the selected node to the new ones

I hope it's clear what I mean. This should work for angles bigger or equal to 90 degree.