Dr Mercola has changed position going from Keto to a more Peat centered approach. His suggestion was to go slow because as you mentioned above Cari starting with sugar in your coffee and gradually increasing the levels as your body becomes accustomed to the shift in the carbohydrate levels in the diet.
In the case of the Carnivore friend you have, if honey would be to big of a change. They may need to go even simpler, slower and with lower amounts more frequently. The suggestion he made was to use glucose mixed in water and sip on it slowly throughout the day until the body adjusts. Dextrose is I believe pure glucose or almost pure. But this may be the route they need to take depending on their situation.
Author
J.R.K