Careful with that. Prey too big too early can cause a lot of back problems later on, this is common in monitors and other large lizards that are carnivorous. What happens is basically when the lizard swallows the prey, it puts a lot of pressure on the spinal cord. This can result in paralasis in the hind legs primarily, but of course death is also possible, and it doesn't sound like a good way to go!
So just stick to a varied diet of insects for the time being, your lizard will be big and tough in no time, then you can try the pinkies :)