Any tips on how to do this? I tried adding a line to default_keywords in 4cpp_default_keywords.h but it doesn't seem to have done anything.

I've gotten this question a few times. The API is a bit obtuse really, so I'll definitely improve it, but this weekend I'll make a quick video to explain it and I'll release a little helper file to get you started.

cool, that would help, thanks :)

This video gives a quick guide on how to do this:
https://www.youtube.com/watch?v=qoEvc4uC9Uw

The new files are available on Patreon:
https://www.patreon.com/posts/4-0-20-super-11668955