I recently lost a nursing doe to bloat (made a feed recipe change that was disastrous, I lost my best eaters before I discovered the problem, and learned about baby gas drops--we saved the last bloat victim with it.) Anyway, the doe in question still had orphan kits that had never left the nestbox, eyes just opening at 10 days of age. I had no litters to foster them, and gave them no chance of survival at that age.
I bought a can of canned evaporated goat milk, put a little of it in a cup, and added a pump of NutraDrench (I understand the bunny version is called NutriDrops, but we still had several bottles of the sheep version with the pump dispenser. I've raised many a lamb on this mixture). I used an eyedropper, and fed the two remaining kits. With lambs, you look for a rapidly wagging tail to know they are eating well, with the bunnies I looked for little air bubbles going up the eyedropper tube, showing the kits were drawing milk out of the tube.
I didn't add cecotropes, and the BeneBac I ordered took almost a month to arrive, so it didn't help. I put CalfManna pellets out and fresh third cut hay for them, and amazingly they survived. A little before they were a month old, they decided they had no interest in the milk anymore. They were eating well, and I just gave them a bit of NutriDrench for a little longer. They're now two months old, happy and healthy. After so much loss, it was a delightful surprise.