Can I change pixel aspect with axes_grid

Usually imshow(arr, aspect='auto') or imshow(arr, aspect=2.0) will
display the image with pixels having some aspect ratio other than 1:1
However, I cannot get this to work when using imshow within an AxesGrid axis.
Is there a way to get an array shown with imshow() within an AxesGrid
axis to have a pixel aspect other than 1:1 ?
If not, is there a simple way to add a shared colorbar when using subplots() ?