Prepare an ice-water bath. Bring a medium pot of water to a boil. Add 1 pound peaches, and cook for 1 minute. Transfer to ice-water bath to cool. Remove peaches from water.
Peel and halve peaches, and remove pits. Slice peaches into wedges, and transfer to a medium bowl. Toss with orange liqueur, sugar, and salt. Cover, and set in a warm spot until peaches give off juice, about 20 minutes.
Puree peach mixture in a blender or a food processor until completely smooth. Immediately stir in tequila and lemon juice. (Peach puree with tequila can be refrigerated, covered, for up to 4 hours.) Transfer to a pitcher, and stir in peach nectar.
Fill each of 8 tall glasses with ice, and garnish each with a mint sprig. Cut the remaining 2 peaches into 8 thick wedges, cut a small slit into inside curve of each wedge, and place one wedge on rim of each glass. Divide margarita among glasses.
The peach wedges used as a garnish should be slightly firm, but still ripe, so they can easily be perched on the rim of the glass.