I give each visitor who signs up to my Google Form an unique url to my landing page for them to share with their friends. The idea is the more they share and their friends visits the site through their given unique url, I'll move them up the waiting list for a product launch.
So for each visitor I gave them example.com/?ref=uniqueCode which is unique to each visitor. Currently I'm using Google App scripts to programatically generate individual url to each visitor who signs up my Google Form.
The goal is if I see traffic coming in from eg: example.com/?ref=a, and I know tag a belongs to John Doe, I'll move John Doe up the waiting list.
Tried googling for a solution but couldn't find any. All solution directs me to creating a particular campaign in Google Analytics with the URL building which really isn't the right solution for this purpose.
How do I set this up with Google Analytics and track the incoming traffic for each unique code of the ref tags of each user?
Going over your question I cannot see why URL builder does not fit your needs.
However, when it comes to immediate and accurate statistics of incoming referrals you may also use a server side script to track incoming visitors.
Also for lots of existing CMS there are plugins to track referrals. If you use a CMS please update your question.