Leader Trait to Make a Luxury Give More Happiness

[Delphi Augustus]

I'm currently trying to figure out how to make a leader trait that gives more happiness (e.g. salt gives double happiness to a specific leader). I've looked at the relevant XML, and it looks like I can change yields (production, culture, etc.), but since happiness isn't considered a yield I can't do that. And I don't want to just straight-up modify the resource, since I only want it to happen for my single civ (with my single trait). Is there any way to do this, or am I out of luck?