There is no public API for this. Any recommendations that will be given may be violated when Apple makes changes to the basic scroll structure.
However, this does not stop you from creating your own scroll indicator from scratch. I needed to do this in a specific case, when the scroll indicator was to be visible at all times, and not just when the user touched the scroll.
You can have your own scroll indicator indicator and position it where it should be based on shifting the contents of the scroll and its scrolling. Adding a handler to scrollViewDidScroll: allows you to correctly position it and take advantage of any inertia that has the form of scrolling.
You can even compress the size of the scroll indicator view depending on how far the user scrolls beyond the size of the scroll content to give the same imitation effect as Apple's implementation.