Breaking equation in align enviroment to put textwidth matrix in separate line

I have to put a textwidth pmatrix into an align environment. When using split, it destroys the centered alignment of the other equation.

Pseudocode:

\begin{align}
\vec{a} &= \vec{b} + \vec{c} \\
\vec{c} &= \operatorname{Matrix}(Variable) \cdot \vec{d} \\
\begin{split}
\operatorname{Matrix}(Variable) &= \\
\begin{pmatrix}
textwidth matrix
\end{pmatrix}
\vec{e} &= 2 \cdot \vec{a}
\end{align}


Without the split the equations would leave the page. With split the equations are aligned left except the right aligned split part.

The result should look like:

      XX=XX
X=X
XX=XXXXX
XX=
XXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXX
XX=XXXX

-

\noalign can be used to put unaligned stuff inbetween:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
\vec{a} &= \vec{b} + \vec{c} \\
\vec{c} &= \operatorname{Matrix}(Variable) \cdot \vec{d} \\
\operatorname{Matrix}(Variable) &= \\
\noalign{$\begin{pmatrix} \rule{.9\textwidth}{1pt} \end{pmatrix}$}
\vec{e} &= 2 \cdot \vec{a}
\end{align}
\end{document}


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