This should be really easy, but I'm having some unexpected problems making it work in version 9. It works fine in version 8.5.
The basic idea is that you create your 2-rail sweep for the spindle, then create a small oval shape with a thickness of whatever you want. Place the oval on top of the bulge with a combine mode of "subtract". That will give you the indentation.
For some reason this isn't working in version 9. I'm going to recreate the file and try again.
D&S Artistic Woodworking http://www.dsartisticwood.com