As for plants, they are great for feeding fry and tadpoles but they really need to be in the tank for a while. What happens is the plants provide a place for micro things to grow, algae, plankton, artemia and other things that fry and other hatchlings can feed on. Another option is a well seasoned sponge filter, doesn't sound like it would be beneficial but the surface area allows for the growth of massive amounts of small food items to grow to feed hatchlings. Just have to leave it alone even when it starts to look a little "nasty". Not the best choice but an option.

For a standby, put some fish food in a blender or small food chopper and turn it into a powder.