A week to Ten days with out gold fish will get him hungry enough to try something "new" with out hurting or starving him to death!!
It will probably be harder on YOU than the fish
Krill is good, I can't get Silversides around here, bigger chunks of Squid are good (like Aqua-Yums), also try whole-frozen-raw-with shell and everything-Shrimp (sized for your Lion, Not those 4" prawns
) I add Selcon and Multi-Vit, if I put garlic on it he won't touch it.
Rather than "waving" a chunk of food on a stick at him while he's "hanging"out in a corner somewhere, You may want to wait until he's active, moving about, "hunting". Usualy alittle after lights out.
Also, they would rather grab it out of the water colum than off the bottom or off a stick. So when he's out hunting, take a piece of Krill/whatever and flick it/splash it lightly on the water till you get his attention-watch his eyes- and then release it into the current, as it flows past him he'll generaly find it irresistable to strike. Unless he's just not hungry, then he'll just "watch" it float past.
If he's not showing "any" interest in food then you have a problem.