I was looking for a homemade baby mouse formula here, but this doesn't seem to be active, so I decided to post what I know about orphan fostering-
I have successfully raised orphan squirrels & etc... for many years.
My parents just rescued a cat who slipped outside and brought them back a pinkie mouse.
I did the same thing I had previously done for the others, and so far "Sherman" is thriving.
I had KMR in the can (kitten milk replacement), a small syringe, and the nipple off a small animal feeding bottle which i squeezed onto the tip of the syringe.
I put Sherman in a shoebox with napkins and cotton balls and place it on a towel, and put a heating pad under the towel on low (DO NOT LEAVE ON UNATTENDED!!!!!). Make sure it is not too hot!
I fed Sherman every 2 hours warmed up KMR. It is very sloppy and will take awhile to get used to doing this so don't be discouraged.
After feeding, i take a cotton ball with warm water and cleaned off her face, belly, and bum- very important to rub bum because that is how mom would encourage urination/defecation!
Sherman seems to be a very healthy and happy little girl so far!