For all my baby racers, once they hatched out of the eggs i put them all in the same 40breeder tank. In that tank i used cypress mulch as a substrate, but i made a mound of it in the middle of the tank with a flat top sort of like a platoe. at the top of my mound is where i placed my basking lamp.
Once i saw all the baby racers lined up next to eachother with their heads raised i tossed a few live pinkies in and left the room for about 20 mins. when i came back i could tell which ones ate and which ones didnt.