Just STOP giving him the Pedialtye. Don't buy any more... and when it runs out just tell him. Sure maybe he will scream/tantrum, but he will forget about it.
Pedialyte and juice is not the same thing. 3 cups of Pedialyte a day, is a LOT for a baby... even if it were juice, 3 cups a day is a lot, for any child/baby.
Pedialyte is for when the child may be dehydrated, and is not to be given as a substitute for a drink. When the child is febrile (feverish) or dehydrated from excessive vomiting or diarhea, it is recommended because it rehydrates and has essential electrolytes. Think of it as a cold medicine. You would give it to your child only if he/she has a cold and not at any other time.
Also, would you personally drink Gatorade, everyday? Gatorade and Pedialyte are drinks that have a specific "purpose." Not meant to be a regular everyday "beverage."
I would give him more water... or juice diluted 50-50 with water. The more "sweets" a person has.... the more they will want it. Per my Pediatrician... and she said that "juice" is not necessary...nor for nutrition. If a child eats well and balanced, "juice" is not needed.
Here's a link:
All the best,