How to preserve the equations alignment in addition to controlling the columns spacing across different nested aligning environements?

Question

In this MWE, I need to preserve the equations alignment at both prescribed positions (i.e. equal signs and \text{}) while controlling the columns spacing (i.e. \qquad).

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{mathtools}
\begin{document}

\begin{alignat}{2}
%
a &= 1 & \qquad &\text{in } \Omega\\
b &= 2 &&\text{on } \Gamma_1\\
%
\shortintertext{and}
%
\begin{alignedat}{2}
c &= 3 && \text{on } \Gamma_2\\
d &= 4 && \text{on } \Gamma_3\\
\end{alignedat}
%
\end{alignat}

\end{document}

Answer 1

More of a hack than a solution:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{mathtools}

\begin{document}

\begin{alignat}{2}
%
a &= 1 & \quad &\text{in } \Omega\\
b &= 2 &&\text{on } \Gamma_1\\
%
\shortintertext{and}
%
\MoveEqLeft[-2.95]\mathclap{\begin{alignedat}{2}
c &= 3 &\qquad&\mkern2mu \text{on } \Gamma_2\\
d &= 4 && \mkern2mu\text{on } \Gamma_3
\end{alignedat}}
%
\end{alignat}

\end{document} 

Edit :

A somewhat neater solution consists in adding \notag for the last two alignments and an empty (numbered) alignment between these last two, compensating for the supplementary vertical spacing:

   \begin{alignat}{2}
    %
    a &= 1 & \quad &\text{in } Ω\\
    b &= 2 &&\text{on } \Gamma₁\\
    %
    \shortintertext{and}
       c &= 3 &&\text{on } \Gamma₂ \notag\\[-0.5\baselineskip]
        & \\[-0.5\baselineskip]
    d &= 4 && \text{on } \Gamma₃ \notag
    %
    \end{alignat}