[pygtk] CellRendererButton, or how to pack a Button inside a TreeView

[Federico]

Hi all,
Is there a way to embed a Button inside a TreeView?
I've tried creating a custom CellRenderer but could not find the way
to paint the button inside it.
I'd like this button to have RELIEF_NONE until it is hovered, then
showing up as a normal prelit button.
Is this possible?

Feel free to suggest a different solution and to ask for more
information if that's not clear :-)

Thanks,
Federico