The pics of the Toelke bows that I have seen have a thumb rest like a Fedora but not a palm swell unless I am mistaken. The hand tracing that many bowyers use seems to be more for the circumference made by the thumb and index finger grip, I am guessing.
Kirk has the right idea about a mold of the grip.
By the way,from what I have seen of modifications of household items made for people with hand arthritis by occupational therapists, a "chubby grip" could be better for those who have arthritis in their bow hand.