Yeah. In order to make it really work well, I might have to descend into the CSS tmLanguage since the HTML language just includes the rules for CSS form the CSS.tmLanguage file. The CSS.tmLanguage isn't designed to expect such things.
That is really how the HTML is doing the embedded code. It is literally just including the scripting language's tmLanguage file. There might be a way to make the the scripts recognize the defines as such without altering the included languages, but I would have to spend quite a bit more time analyzing the dynamics of the rules and figuring out how to insert the new rules to be picked up. It is pretty easy targeting the comments because they are so different than the syntax of most languages.
I am not used to using these kinds of defines; therefore I don't really know all of their rules and usage at this time, so it is hard for me to really put something together at this time.