Upon popular request, we have implemented support for scrollbars on any axis in Highstock 4.2.6. We pulled out the scrollbar logic from the Highstock navigator, making it modular and reusable for datetime, numeric, logarithic and category axes, whether vertical or horizontal.
The full documentation and available options can be seen in our API docs for Highstock.
But the scrollbars are not limited to stock charts or Y axis. Using the highstock.js file, it can be applied to regular Highcharts axes too. See examples of: