I’ll have to look up and find out how else he recommended it. He was an interesting fellow. I was brought up to scorn anything that was not standard/orthodox/modern/secular etc. My mother mentioned him with scorn.
Sometimes the apple DOES fall far from the tree, maybe a changeling...
Years ago I was involved with the A.R.E. because some friends were taking the massage therapy courses in Virginia Beach. They were telling me some of the uses of castor oil, very much like your method.
https://www.edgarcayce.org/the-readings/health-and-wellness/holistic-health-database/