you put the food in for 10 minutes walk away, if they do not eat in those 10 minutes you pick it up and feed at dinner time.
You must break them of the habit, and the only way is to become a bit harsh on them.
I use to have a Presa that ate that way ... matter of fact he wanted me to hold the bowl. He did not eat for 2 days .. when he got hungary enough he figured out I did not have to be there and he started eating.
"In order to really enjoy a dog, one doesnt merely try to train him to be semi human. The point of it is to open oneself to the possibility of becoming partly a dog."