Markup Control ScrollViewer

I currently update a Markup controls caption using a timer. The XAML markup includes a ScrollViewer, and I would like to be able to get the thumb position of the scrollbar so that I can restore the position of the thumb after updating the content, otherwise if the user has scrolled away from the top of the page, the view gets reset to the top of the page after changing the Caption property.

Is there a way to get & set the position of a ScrollViewer thumb? If not, another option would be to set the VerticalScrollBarVisibilty attribute to Disabled and then roll my own scrollbar. But this would require the ability to get the Height of rendered XAML in the Markup control. Is there a way to do this?

To recap:

1) Is there a way to get & set the position of a ScrollViewer thumb in XAML?
2) Is there a way to get the rendered height of XAML in the Markup control?
3) If the answer to both of these questions is curently NO, is there any chance on either or both of these requirements to be implented?

Thanks in advance.

Ok, last addendum. I see that you can use the MarkupContext property to create markup objects and then add then to the Markup control. Unfortunately, while many objects exist (like MarkupTextBlock, for example), there is no corresponding MarkupScrollViewer object. I guess I would need this to be able to programmatically interact with the ScrollViewer scrollbar.

Excellent news Oleg! Thanks a lot...
Is there an updated beta that I can try?