异步调用Codeigniter控制器方法

I have this scenario:

    ----------    1.Call  /register              ---------  3. Async call to
   |  My PC   |  -------------------------->    |My       | ------  
   |          |   2. Server returns view        |Server   |        '  /welcome
    ----------   <--------------------------    |         |       ' 
        |         4. returns welcome message    |         |      ' 
       ---       <--------------------------    |         |     '
                     getting it from 3          |         |   '
                                                 ---------  <'

1. I call my register method within the User controller

2. Server processes registration data and render view by $this->load->view('template_path'); But I dont want it to finished up right there! I want another method within the User controller be called----(3)

3. Server asynchronously calls user/welcome which returns some welcome template view

4. The view that comes from 3 will be shown on a modal which is hidden within the rendered page from response 2 and be shown when modal contents are available from this(2nd) response

How can I do it? Any ideas?