Good PHP developer needed for REFERRAL SYSTEM (codeigniter)

General information for the website: Gaming community

Kind of development: Customization of existing website

Num. of web pages/modules: 1 module

Description of every page/module: The site is based on a CodeIgniter CMS.

Module description:
1 - So I have a link to share : mysite.com/floman
2 - I share it on a forum and someone clicks it.
3 - The visitor lands on my homepage (important to have this)
4 - He visits a bit and goes on every page of the site, and then he decides to click on the register button. He registers a new account.
5 - He is now my referree/referral and I am his referrer and I get a reward (virtual currency/points) because a new person registered thanks to me. So it must work either with cookies or php session.

Description of requirements/features:
Global referral system working on the whole site (with php session or cookies or something better if it exists)
Prevent same IP abuse (with IP check and cookie check)
Add a leaderboard for most shared links and extra rewards (optional)

CMS and Admin requirements:
CodeIgniter (old version)
Smarty (tpl replacement for html)
SQL knowledge
Good english required

Similar urls: http://ergodriven.com/topo-sharing/

Extra notes:
The idea comes from that https://sumo.com/stories/diy-crowdfunding
I attached some files to look at from that project if you're curious (there is php made from scratch there, not using a CMS)

I'll send the actual CMS in private