### polynomial with matrix coefficients

Is there a way in sage to work with polynomials or power series over a ring of matrices? For example, I can write something like:

z=var('z')
A=matrix([[z^2+z+1,z],[0,z^2]])

But then lets say I do some transformations and want to recover from the result the matrix coefficient of a particular term. With the matrix above I can write something like

A[0,1].coefficient(z)

or

A[1,0].coefficient(z)

to try to get the individual entries. But what I want is a function that takes A.coefficient(z,2) and returns

[1 0]
[0 1]

Is there a way to do this?