Fix tag placement in align environment when locally switching from reqno to leqno

Question

I have been using the solution in Tag placing with amsmath to turn on the leqno option locally for part of a document. However, when using the align environment from amsmath, this leads to spacing problems: the aligned equations are still shifted left to make room for a tag on the right, with the result that they overlap the tag placed on the left. How can I tell amsmath to process the align environment in the same way as if I had specified the leqno option in the documentclass?

MWE:

\documentclass{article}
\usepackage{amsmath}

\makeatletter
\newcommand{\leqnos}{\tagsleft@true\let\veqno\@@leqno}
\newcommand{\reqnos}{\tagsleft@false\let\veqno\@@eqno}\makeatother

\begin{document}
\reqnos
\begin{align}
    1+2+3+4+5+6+7&=7+6+5+4+4+3+2+1
    \tag{Boring Equation}       
\end{align}
\leqnos
\begin{align}
    1+2+3+4+5+6+7&=7+6+5+4+4+3+2+1
    \tag{Boring Equation}       
\end{align}
\end{document}