Getting accurate referrals from arbitrary sites analytics.js - google-analytics

Question

Working on a web app where at step 2 the user leaves to her domain and comes back. The domain she leaves to is dynamically entered into our form (this step is required for an OAuth token flow).
So we're having that domain appear as a referrer and want to keep the original referrer in Google Analytics.
Used to be (with ga.js) you'd just pass utm_nooverride=1 in the callback URL coming back to your site, but we're using analytics.js.
Linker Params won't work because we can't dynamically control the callback URL.
So: Questions:
1) Does the excluded referrers list in GA for a web property allow regular expressions? It allowed *.sample.com to be saved, but I haven't tested whether it works or not yet.
2) Or is there an API call to our GA account we can make to add dynamic excluded referrer domains on the fly?
Any other way to solve this?

Answer 1

Long time no seen, funny to find you here.
Now for your question, I see 2 options,
The Referrer exclusion list doesn't support regexes. But it does exclude all subdomains. So if all the domains you are interested in removing are subdomains of something specifically you can remove only the top level domain and should be good. More Info
There's a trick you can use to force analytics.js to not send the referrer to GA if you don't want to. You can manually set the referrer to an empty string on that page. You can do it always or when it matches the user entered hostname. It would look something like this:
var hostname_to_ignore = 'site.com';
ga('create', 'UA-XXXXX-Y', 'auto');
if(document.referrer.indexOf(hostname_to_ignore) > 0) {
ga('set', 'referrer', '');
}
ga('send', 'pageview');
Not sending the referrer will keep GA from creating a new session and it should just continue the previous session if the last hit was less than 30 min ago. That's probably what you want. I didn't test this, it's possible that setting it to null or undefined is even better, I would try it out and check what the hits look like.
More Info