I've used this formula for pups I had to wean early (for one reason or another), supplementing newborn pups, as well as for sick dogs that couldn't eat solid food. I've currently got a 12 day old raisin-face on it and he's gained quite a bit every single day. Looks more like Fat Albert than a Neo!

This works better than anything I've ever bought in the stores already prepared.
Put 6oz water in a pan to boil
In a blender, combine the following:
1 12oz can evaporated milk
1 Tbsp light corn syrup (Karo)
4 Tbsp whole yogurt "Dannon Plain Whole" (NOT low or non fat)
2 egg yolks
Put blender on lowest setting. after a few seconds, you can remove the lid
and add:
2 packets of unflavored gelatin ("Knox" found in the canning section or near the Jell-o)
wait about 10 seconds, then add your 6oz boiling water. Wait another 10
seconds then turn blender off. Pour into container and allow to cool, then
refrigerate.
It's called "The Gloop" because after it cools, it becomes a gel. It's easy
to scoop it out of the container with a spoon. You heat it up before serving
to the pup and it becomes a liquid again.
I double up on the recipe and store it in a clean, 2-liter bottle. It's easy to turn upside down and squeeze out what you need. Keep in the fridge and any left after 7 days, just feed it to one of the big dogs and make some fresh.