Is there a reason why your only sticking to frozen foods? You could find plenty of freeze dried foods like krill or pellets that float to train him on.
Don't think you understand his post. Im sure the frozen bloodworms he gets float while they are FROZEN. Underneath his first statement he says he needs something that will float after they melt/thaw and come apart.
That's really tricky and I know of no such frozen food. After a little while all frozen food will thaw and end up sinking. Couldn't you just break off a small piece and have him eat it while it is still frozen? Frozen krill works well. Seriously though why not just use pellets?
I feed my fish with cichlid pellets. They go crazy for it. Fish are usually scavengers and will eat anything that comes their way, even though it can harm their health to overindulge. So it is essential to feed them the correct food with the correct dose in order to make them grow.
I see... I got an idea... If you really want him to eat floating foods FORCE him to eat pellets/freeze dried. This is the reason why when I buy an aro from my LFS I make sure they are feeding him pellets/flakes/prepared foods and they are eating them well before I buy him. I also look that they are ravenous and will follow my hand and are not shy. That way if i want to feed him frozen (I almost never do though. I always stick to pellets, maybe VERY occasionally he gets some frozen foods), he will still follow my hand and look up waiting for the food to drop and smash/eat it right away before it even has the chance to melt. Good luck with your aro.
Here's a tip next time you buy an aro. If the pack of baby aro's are shy tell the LFS owner you are interested/will buy an aro on one condition. He gets a pellet or flake and drops it on the opposite side of the pack of aros. The first one to rush out and eat the flake/pellet is the one you will buy. If they all rush it and try to eat the flake/pellet pick the nicest and most responsive one. Works for me every time.