I don't think it works like that. A lot of aphids will only use certain host plants. And even if they did decide to go for the hibiscus, I don't know if they would still have any toxic stuff left over from the milkweed.
Maybe try checking for some wild cabbage/mustard plants? I find tons of aphids on those when it gets cold. They huddle together.
Edit: You could try culturing wild fruit flies, but those are a huge pain in the butt since they can fly everywhere and your house will have them all over the place. I would just buy a culture of flightless fruit flies or pinhead crickets.