I'm looking to switch mine over to rats as well, but I was told that it helps to make the rat smell like a mouse- either by rubbing mouse bedding on the rat, or even thawing the two together.
Dante is still intimidated by the rat as yours is, but I was told to wait a bit longer until he's more established weight-wise, and can comfortably miss a meal or two. But like others have said, some never take a mouse.
1.0 Pumpkin Pied BP
0.1 Bearded dragon
1.2 Leopard gecko
0.1 Ornate Pacman Frog