Widgets on top of FigureCanvas

I would like to put a gtk.Button on top of a FigureCanvas. But whatever
I try the FigureCanvas stays always on top hiding the button.

Below is an example where I can change the order of buttons
by switching the following two lines

   lay.put(but1,360,260)
   lay.put(but2,360,275)

but this doesn't work for FigureCanvas

  lay.put(canvas,0,0)

Any help appreciated.

Ciao
Andreas

import gtk
import numpy as np
import pylab as mpl
from matplotlib.backends.backend_gtkagg import FigureCanvasGTKAgg as FigureCanvas

win = gtk.Window()
win.set_default_size(450,350)

fig = mpl.figure()
subfig = fig.add_subplot(1,1,1)
ax = subfig.plot([2,3,1])
canvas = FigureCanvas(fig)
canvas.set_size_request(400,300)

but1 = gtk.Button('111111111')
but2 = gtk.Button('222222222')

lay = gtk.Layout()
lay.put(canvas,0,0)
lay.put(but1,360,260)
lay.put(but2,360,275)

win.add(lay)
win.show_all()
win.connect('destroy', gtk.main_quit)
gtk.main()