Well, you may have better luck going that route than I have. I've always picked out the runts, but not for the same reason you would. I've always picked out the runts because I felt sorry for them. My little Muffin was the runt of her litter, too. I felt so sorry for her chasing her litter mates trying to get the toy they all kept exchanging, but she was always too little to get it. So I took her home and told her she could have all of the toys her little heart desired. And so it was. She also outgrew being a runt. She was 9 lbs or more...depending on her weight at the moment.
Kacee was the runt of her litter, too. She also outgrew the mini stage and is now a whopping 8 lbs!
P.S. They both would be categorized as very healthy, too.