Plugin doesn't work when WordPress admin isn't on default place

I installed WordPress as Git submodule so the path to wp-admin is /wordpress/wp-admin. This breaks the plugin. It’s hard coded on that path.

The plugin isn’t maintained anymore. I can pickup the maintenance, but than I need access to this plugin. Does anyone now how to contact Joel Starnes? The url provided in the description (http://joelstarnes.co.uk/contact) doesn’t work.

https://ww.wp.xz.cn/plugins/postmash/