firstname lastname for aditional authors in bibtex

firstname lastname for aditional authors in bibtex

I am still struggeling with the de gruyter citation style. I know that I
can produce one from scratch with tex makebst, but I have one that is
almost working and I had to make a lot of funny changes, which I had to
redo on the automatically created file.
The editors require me to have `Meier, Max and Klaus Meier 2009 My first
paper ...
\documentclass{article}
\usepackage{filecontents}
\usepackage{natbib}
\begin{filecontents}{SM.bib}
@article{a, author={Max Meier and Klaus Meier}, title={My first paper},
journal={Journal of Googelology},
volume=3123, number=1, pages={3--45}, year=2009}
\end{filecontents}
\begin{document}
\nocite{*}
\bibliographystyle{degruyter-hsk}
\bibliography{SM}
\end{document}
I know it is format.names, but how do I do it?
De Gruyter .bst is here: degruyter-hsk.bst