This is certainly doable, and seems like a fun challenge, but I won't have a day off to mess with this until this weekend. That said, you have enough information here that I imagine that you can get this done on your own before then. The above script is already getting the scroll pane from the dropdown as well as the list renderer, so it's not that big of a jump to get the vertical scroll bar and set its value to a list position. There are numerous examples of scroll position manipulation in the forum. As far as setting the item selected, that should be doable too.
Here are a few related examples from the forum to get you started:
• Example of scroll pane and scroll bar manipulation
• Another example of scroll position maniptulation
• An example of dropdown rendering manipulation
When you get this working, report back. We would love to see what you come up for this.