XeTeX ⇒ Where to get an upright sans-serif math capital Greek without changing the rest?

[user49915]

Feeding the code

\documentclass{article}
\usepackage[ngerman]{babel}
\usepackage{mathtools}%%% loads amsmath internally
\mathtoolsset{mathic=true} %%% See http://tex.stackexchange.com/a/3496
\usepackage[math-style=ISO]{unicode-math}%%% In general, we wish to have ISO style.
\setmainfont[Ligatures=TeX]{TeX Gyre Termes}%%% Times in general.
\setsansfont{TeX Gyre Heros}[Scale=0.88]%%% scaling somewhat ok.
\setmonofont{TeX Gyre Cursor}%%% no explicit turning on ligatures for the monospaced font.
\setmathfont[Ligatures=TeX]{TeX Gyre Termes Math}%%% Times-like math font.
\newcommand{\concreteSort}[1]{\mathsf{#1}}
\begin{document}
\begin{tabular}{ll}
Normal math italic Latin:& \(Sigma\).\\ %%% product of five variables S, i, g, m, a.
Normal math italic Greek:& \(\Sigma\).\\ %%% a single variable.
Upright sans-serif math Latin:&\(\concreteSort{Sigma}\).\\%%% a constant with a fixed meaning.
Upright sans-serif math Greek:&\(\concreteSort{\upSigma}\).%%% another constant with a fixed meaning. Where to get an upright sans-serif math Σ without changing the rest?
\end{tabular}
\end{document}

to xelatex leads to

mwe.png (30.37 KiB) Viewed 13769 times

As you see above, the last Σ has serifs. How to get rid of the serifs for upright math capital Greek without changing the rest, i.e., maintaining the formatting of the remaining text and math? Yes, we wish to stay with [xe|lua]latex. I expect that a different font is needed, but which one? How to switch to it only for the upright capital Greek math letters? Ideally, \concreteSort should produce the same (upright, sans-serif) formatting for Latin and capital Greek, but it doesn't.

Crosspost: http://tex.stackexchange.com/questions/537208