Kerry asked me if he had discussed it in Montreal when I took his ganache course. The description above is not what I remember, but maybe we are talking about a different chocolate. ( I am thinking of the small log with a fairly wide stripe, see image below.) For that chocolate, he mentioned that his assistant used a thin strip in each cavity to block off before spraying, and that it took a fair amount of time. We discussed in the group how this wouldn't be effiicient for production. He arrived in Montreal with all the molds ready to be filled.
Here is a picture of both chocolates. The one on the left below was done with a thin strip. We didn't discuss the half dome, which must be the one you are talking about?