Adding custom keyboard shortcuts to sub-menu options of Chrome extensions?

So I found a nifty little Chrome extension that allows me to save a web page, a group of tabs, or even the currently selected text on the page as Markdown. I rarely clip the entire page, and often use the “Copy Selection As Markdown” option within the extension’s sub-menu.

However, having to right-click the text, navigate to “MarkDownload”, then to “Copy Selection As Markdown” option is quite cumbersome – especially if I’m on a rampage clipping a bunch of stuff.

I tried adding a custom keyboard shortcut via System Preferences under Keyboard > Shortcuts, but it didn’t seem to work for menus and options for the right-click dialogue that pops up.

Does anyone know of a way to add a custom shortcut to these menu items? Or am I going to have to create some advanced KM macro for this?

Thanks in advance for your help!