I would assume that you would hand feed them and care for them like any other rat, so on that principle (just my opinion by the way) I found this great page.
Caring for Orphans
This article was taken from the AFRMA Breeding Rats & Mice, Care and Guidelines book.
As far as a formula to use, many people have used different ones to their advantage. Whole, raw, fresh goat milk; KMR® (Kitten Milk Replacer); Esbilac® (puppy formula); Enfamil (without iron); or Soyalac human formula have all been used. The powdered formula is usually used rather than the liquid as you can mix up a fresh batch each day and the powder will last longer. The liquid formulas have to be used within 3 days after opening. Lambert Kay™ makes a Mother’s Helper™ puppy formula that can also be used for rats and other orphan babies.
A baby bird feeding syringe with a fine curved tip or a very small doll nursing bottle will work as a nurser. You can also use a piece of absorbent string, acting like a wick from bottle to baby, for the very small ones until they are big enough to grasp the bottle tip itself. Another idea is to take a piece of small plastic tubing (strip the plastic tubing off a piece of wire—22 or 24 gague for mice; 14 to 20 gague for rats) about ½ to 1 inch long. You can then insert this tubing into your syringe or nipple of a nurser bottle. Four Paws® makes an Easy Feeder™ Hand Feeding Syringe For Small Animals that has two syringes in the pack—one with a nipple tip and one with a tapered tip. The tapered tip syringe has an opening equivalent to a size 12–14 gague wire tubing. The baby bird feeding syringe has a tip equivalent to a 22 gague wire tubing. Also, you can get a gluing tip from a hobby/beauty supply store. Heat up the tip and slip it on the syringe. This will “glue” it to the syringe.
Feed small amounts at each feeding, being careful not to get any in their lungs (if you see milk bubbling from their nose, it’s an indication some is getting into their lungs). Always feed warm (not hot or cold) formula to your babies.
You can tell when their tummies are full by the white patch in the left middle of their bellies (do not overfeed). It will take about five minutes to feed each one.
. . . you will need to feed them EVERY 2 hours, so be prepared for some sleepless nights.
Don’t be discouraged if they appear smaller than others their age. This is common with hand-raised babies. Sometimes they will even lose their hair for a short time, but it will eventually grow back.
After you feed each baby, they will need you to massage their abdomen and rectal area with a warm, damp cloth to stimulate them to urinate and pass solid wastes. You will need to do this until they are eliminating on their own. Remember to always handle these guys carefully as they are very small. It is very important to keep these little guys warm at all times. Many people use the plastic critter carriers lined with a towel and either a hot water bottle under the towel or an electric heating pad (set on the lowest setting) with the carrier placed on it. (The temperature of the nest should be between 75°F (24°C) and 90°F (32°C).) This makes it easy to take them with you to work or school to feed them on their schedule.
Diarrhea is one problem you may encounter when feeding these small rodents. The main cause is overfeeding. Another cause can be coccidiosis—a one-celled internal parasite that can be diagnosed by your veterinarian. Dehydration occurs with diarrhea no matter what the cause and can kill the babies if not treated promptly. You will need to stop giving all milk to your orphans and replace it with the same amount of electrolyte solution for human infants. Milk will irritate the digestive tract and prolong the diarrhea. Your babies will need, not only the fluids from the electrolyte solution, but also the salts and chemicals it contains. It will often be necessary to also give a few drops of kaolin-pectin every 2 hours to help halt the diarrhea.
Once the babies open their eyes, you can start adding dry baby cereal to their formula (make sure it will pass through the tip of the nurser) as well as cutting down on the nightly feedings. You can start to wean them off the bottle and onto a dish when they are about 3 weeks old. Dip your finger in the gruel mixture and let them lick it off your fingers. Decrease the amount of bottle feedings and give their meal in a small dish three to four times a day. You can start to add different things like oatmeal, bread, lab block powder, and baby food to their mixture. Also by this time, they will start to nibble on bits of apple, carrot, fruits, seeds, etc. Make sure fresh water is also available at all times as they will start to drink from a bottle. Give fresh meals each time, taking out any uneaten foods. You will also need to clean them up after they eat as they are very messy eaters. They can lose their coats and go bald temporarily if they are left dirty.