Passing Custom Variables

I'm working on behalf of a client to implement some custom variables into the LivePerson code. Since I don't have access to their admin console, I need to do all of this in the code.

I found this article:

Implementing Custom Variables

But I have a question -- does the client have to create any new fields within the admin console? Or can I just initiate the custom variables from within the code?

We're trying to pass utm parameters captured from the Google Analytics cookie through to LivePerson. If there is another way to do this that you know of, that would also be helpful.

Thanks!

Kyle