Change states / trigger actions by progress in scroll panel

Hi,

I have the following idea: I have a somewhat lengthy text which I want to put into a scroll panel on a slide. To structure the content I would like bullet points or shapes like rectangles with those bullet point texts to appear when a certain mark in the text is reached, e. g. the reader scrolls to the second paragraph and the first paragraph is summarized in a bullet point next to the scroll panel. When the end of the text is reached, all bullet points are visible.

I know in HTML you can set anchor points. Maybe there is a way to set a variable by reaching a certain anchor point (an I set those in AS?) and trigger the state of the bullet point that way?
Or can I synchronize the movements of the scroll bar with a slider? Triggering the bullet points with a slider is easy...

Working with SL3. Have tried to search the forum but did not find what I was looking for...

Thanks for any ideas!