Have they had their first shed yet? I would probably wait abit longer and then try, dont do too pushy or worried just yet.
When its time you can try a few different methods. Some have had success using the shallow bowl in the way you mentioned, some may take it if offered like people do with pinkies, the ones that dont Ive done what I do with elapids annoy them with it till it bites and hangs on to it. Then as the less prefered and most stressful forcefed, but you are awhile off before considering this just yet.