I have a widget that I worked on while developing CpGears. It laid dormant for a while and lately I finished working on it. The widget is called the Playbar Lock Widget and as its name indicates, it locks the playbar from going forward. So, a learner will not be able to use the next page button or the progress bar to advance in the lesson. However, the entire functionality will return once the presentation reaches the last page.

The widget also tracks the last page visited by the user and if the user goes backward, the next page button will reappear until the user goes back to the last visited page. The nice part is that the widget functionality works also with a LMS. The widget will use the status of the lesson stored in the LMS to enable or disable the next page button and the progress bar.

You can find more information here or experiment with the demo.