I think you'll have better luck at the Disney owned restaurants, such as Cali Grill and The Wave, which tend to be much more liberal with the requirements of the dining plan than the non-Disney owned places such as Via Napoli and Chefs where they are reimbursed by Disney according to the rules of the plan. At those venues, if the item is an appetizer, even though you want it in lieu of an entree, the restaurant wouldn't be reimbursed so it's unlikely they will let you do it.
As a PP suggested, you could pay for your meal OOP and save that credit for a 2 credit dinner show or signature restaurant.