To do it we took little steps. First we would hand feed him kibble. Then every once in a while (like two times a meal) we would get a high value treat and stick it out in our hands. Of course being the _not_greedy little basenji he is he would try to get the treat while chewing other food. While he was distracted with looking at the treat we would stick our fingers in take the food and immediately treat. Repeat until the dog does not seem phased by this at all.
Then once he was comfortable with that, we moved on to the treat in one handwith the hand closed, we let him eat at the bowl and randomly (about 2x a meal) take his head while he is eating, stick our fingers in and take the food out. Then treat immediately. Repeat untill the dog does not seem phased by this at all.
After he was trained like this we reduced the frequency of taking food. Now I just do it once in a while.
To reiterate, I have had Indy since he was 10 weeks old. He is a very easy going guy. So if you have a rescue you might need to go slower, or ask someone else for help. But I can tell you this, especially if you live in an apt complex, people like to throw food on the ground. Mouldy hotdogs, cooked chicken bones, clam shells, stuff like that and Indy has gotten all of this stuff in his mouth, and given it up as soon as I stuck my hands in there. I probably saved him alot of pain and some heart ache and vet bills on my part.
Another time he got a peice of chicken wire in his mouth and was choking, in his state of panick I was able to put my fingers all the way into his mouth, disliodge the wire, and take it out.
I guess maybe he likes to "taste" things more than other dogs but I am not so worried about it since I know he will give it up at any time no matter his mood.