The page linked says "space-separated list of default DNS servers". From this I would assume that this is just an option one could simply overwrite by using a non-default configuration. That doesn't seem so bad, however I could also be misunderstanding and in order to disable these servers one would need to patch the source code like you imply. Do you have a more specific source that would answer this question?

Edit: from the other comments in this thread it seems like it it is a build time option