Welcome Waffles...
That's a good sign that he ate an adult mouse on day one. Personally, I'd try feeding one adult mouse (not 2) every 7-10 days, while his body adjusts to eating on a regular basis. I agree w/ bcr229, to feed wet f/t if he'll accept them, & also adding a probiotic or herp. vitamins would likely help too. You really can't or shouldn't rush getting weight back on a snake like this- just be patient.
I'd do the same things mentioned with stuck shed or eye-caps too. Don't worry about this snake "catching up", just let him gradually eat & rehydrate. Snakes like this need time & "TLC"- I bet he makes a great recovery, thanks to you. Some day you'll look back & wonder if this is the same snake.![]()