Use a conductive mask on your rack which will allow you to rack the part while masking the threaded hole in one operation. They're also re-usable and will take 500F temps.
Custom silicone paint masks made specifically for your part shape and dimensions are available from several companies. The masks will take 500F and are re-usable. They can also eliminate the bridging problem you are having and leave a clean paint line. If designed correctly they can decrease...