I do this while preserving the complete integrity of the head scroll.
My extensions are supported by the scroll; they are held in place by the perfect contact with the back of the scroll and by the pressure of the strings. I will always check the sightline from the fingerboard to see if it is possible to install an extension without modifying the scroll. If not, I advise the client to either quit the installation, or to have the instrument’s neck changed, keeping the original scroll, in order to make the installation possible.
I use only one screw, at the height of the nut, but if possible I prepare a notch to attach the extension directly to the fingerboard – in this case, the screw is not necessary.