So you want three different url paths that point to three different views, but you want the forms to all send their info to the same REST endpoint in the same controller (users#create)? That sounds simple. You have GET requests to get the html/erb files for each registration page (welcome#index, welcome#cool, welcome#coolest), and routes for each to send the GET request to the right controller action.
Then you set up the forms to all send their info to POST to users#new, and one route from there.
Does that make sense?