Freshly hatched artemia (baby brine-shrimp) are probably the best fry food, but you would have needed to setup the hatchery a couple days ago.
Do you have a small medicine dropper?
If you can get the fry into a breeding net, take some flake food, grind it into a fine powder with your fingers, mix it with some water (in a shot glass or something) and administer it with the medicine dropper.