Do you know a waiting list service which rewards sharing?

For the upcoming launch of my Mentoring service, I am searching for a waiting list which supports a sharing functionality.
So basically, users should be ranked by the time that they signed up to the service. First come first serve.
However, users can improve their position if they share the product with others. If their friends also sign up to the waiting list, their rank will improve.

Bonus points:

• if users can tell me their willingness to pay (in addition to their name and email)
• if users can back up their signup with a small upfront payment (similar to Kickstarter)