If I have enough aphids, they’re kind of already enough of a lure. The plan of let them run wild until the ladybugs show up only really works if they’re on mature plants that won’t die in the meantime.

But also, I have better luck keeping them around for longer if I make sure to spritz some water all over the plants every morning/evening after release (until I find eggs on a leaf at least). If they’ve got food and easy to access water, like droplets on leaves, they tend to stick around.