Don't laugh, but I was sooooo desperate to remove that onion smell from my hands that I tried several remedies all at once.
Salt, lemon juice and a metal spoon.
I poured about 2 tablespoons of sea salt into my hand, soaked it with pure lemon juice concentrate, and massaged the mixture into my hand with a large metal spoon. All I needed was a glass with vodka and I'd be a human cocktail. But guess what? It worked. I'm not really sure what did the trick, all I know is that the onion smell is gone. So a big thanks to everyone who wrote in with suggestions.
Now... any suggestions on how to get a salty, slightly metallic lemon smell off of my hands?