Mixpanel last non-direct traffic source

Question

I was following mixpanel's documentation for how to track last known UTMs parameters.

then i noticed it is not useful in cases where the last traffic source is without UTMs such as from google organic, in such cases it will not register google organic as traffic source and will give the last credit to the last known UTM. How can i modify the script provided in the documentation in order for it to register last known non-UTM traffic sources as well? Thanks!

function getQueryParam(url, param) {
// Expects a raw URL
param = param.replace(/[[]/, "\[").replace(/[]]/, "\]");
var regexS = "[\?&]" + param + "=([^&#]*)",
    regex = new RegExp( regexS ),
    results = regex.exec(url);
if (results === null || (results && typeof(results[1]) !== 'string' && results[1].length)) {
  return '';
  } else {
  return decodeURIComponent(results[1]).replace(/\W/gi, ' ');
  }
};
function campaignParams() {
var campaign_keywords = 'utm_source utm_medium utm_campaign utm_content utm_term'.split(' ')
    , kw = ''
    , params = {}
    , first_params = {};
var index;
for (index = 0; index < campaign_keywords.length; ++index) {
  kw = getQueryParam(document.URL, campaign_keywords[index]);
  if (kw.length) {
    params[campaign_keywords[index] + ' [last touch]'] = kw;
  }
}
for (index = 0; index < campaign_keywords.length; ++index) {
  kw = getQueryParam(document.URL, campaign_keywords[index]);
  if (kw.length) {
    first_params[campaign_keywords[index] + ' [first touch]'] = kw;
  }
}
mixpanel.people.set(params);
mixpanel.people.set_once(first_params);
mixpanel.register(params);
}
campaignParams();