This was something that has been mentioned before and that I wanted to do. As you may already know, culture in COL is not very complex. You can set culture to equal any one yield you want in the XML ... I am not remembering which exact file it was ATM. but is basically a simple culture=bells.
I actually had an idea for how to mod it into accepting more than one yield combined for culture, but I didn't write it down and now I forget. If I recall correctly, though, it did involve changing the SDK.
I think it had something to do when I was poking around in there creating a new yield I also made a function (or a method? I haven't looked at the SDK in a month or more and I am not a C++ programmer) in CvPlayer I think but left it empty, it was in here I was going to try to combine them but I think I was having trouble (not being a C++ guy) passing values into the function.
I have a lot to do right now, but if I get any extra time I will look at it and report back.