Custom language syntax highlighting in VitePress

I've recently been trying to add a TextMate grammar file, found here, as a custom language using the integrated Shiki setup in VitePress. I have found this note in the VitePress documentation, which leads me here, which takes me to the declarations in code found here, which tells me to refer to the Shiki documentation, which provides an explanation and example for how to accomplish this if I were to setup Shiki in my own code, which I don't. As far as I can tell, it is internally handled in VitePress and I'm unsure how to access it. The config which I am using for VitePress can be found here. The documentation is vague to me, and I have not yet found a working solution to adding a custom language grammar file into the Shiki highlighting program.