Viewing Restrictions - Access to part of a Blog Post?

Hi Si Team

I am building a template for articles containing webinars.
I use your “page break” plugin to build articles with 4 tabs.
I have built my now buttons to help people switch from tab to tab.

Here is an eg of an article:

http://www.finalbug.net/blog/entry/560-fcp-x-subtitles-the-missing-webinars-03
http://www.finalbug.net/blog/entry/560-fcp-x-subtitles-the-missing-webinars-03?pagestart=1
http://www.finalbug.net/blog/entry/560-fcp-x-subtitles-the-missing-webinars-03?pagestart=2
http://www.finalbug.net/blog/entry/560-fcp-x-subtitles-the-missing-webinars-03?pagestart=3

I am thinking would´t it be cool if a user can view link 01-02.
But be required to register for link 03-04.
This could at some point be hooked up to either a SI Shop or Payplans.

Any ideas on how to achieve some thing like this?

eg some way of saying ?pagestart=3 forces a user to register with profile XYZ on the site.

I would be very grateful for any insights on this.

This is the only thing I found that is remotely similar:

http://stackideas.com/forums/viewing-restrictions-paid-membership-plans

thanks

Paul