Then you can use the information at https://omni-automation.com/omnigraffle/index.html to create a script that will create the objects, get the graphic that you want, and rotate it the amount desired (or to the location desired depending on which approach you take).
If you want to impact the graphic that is selected, you can use the script at https://omni-automation.com/omnigraffle/graphics-00.html for Checking for a Single Selected Graphic.
Ultimately, the part you will change will come down to changing the locations of the line tail on the knob which you can do by specifying the exact points, or by using math in your script. Learn more about automating OmniGraffle Lines at https://omni-automation.com/omnigraffle/lines-00.html.
I hope this gets you started! Happy scripting.