Recipe: How to Freeze Peaches or Nectarines

You can do that with the nectarines but they will darken without the Fruit Fresh/ascorbic acid. You can just mix some Fruit Fresh in them before freezing.
Here are some other options:

FREEZING PEACHES OR NECTARINES
Preparation - Select well-ripened fruit and handle carefully to avoid bruising. Sort, wash and peel.

Syrup Pack - Use 40 percent syrup. For a better quality product, add 1/2 teaspoon (1500 mg) ascorbic acid per quart of syrup. Put peaches directly into cold syrup in container - starting with 1/2 cup syrup to a pint container. Press fruit down and add syrup to cover, leaving headspace. Place a small piece of crumpled water-resistant paper on top to hold fruit down. Seal and freeze.

Sugar Pack - To each quart (1 1/3 pounds) of prepared fruit add 2/3 cup sugar and mix well. Stir gently until sugar is dissolved or let stand for 15 minutes. To retard darkening, sprinkle ascorbic acid dissolved in water over the peaches before adding sugar. Use 1/4 teaspoon (750 mg) ascorbic acid in 3 tablespoons cold water to each quart of fruit. Pack into containers, leaving headspace. Seal and freeze.

Crushed or Pur e - Coarsely crush peeled and pitted peaches. For pur e, press through a sieve or pur e in a blender or food processor. (Heating pitted peaches for 4 minutes in just enough water to prevent scorching makes them easier to pur e. For better quality, add 1/8 teaspoon (375 mg) ascorbic acid to each quart of fruit. Pack into containers. Leave headspace. Seal and freeze.

I have not frozen pears, I can mine, but I hear those packed in the syrup with Fruit Fresh are the best.
Pears
Preparation - Select full-flavored pears that are crisp and firm, not mealy in texture. Wash, peel and core. Slice medium pears into twelfths, large ones into sixteenths.

Syrup Pack - Heat pears in boiling 40 percent syrup for 1 to 2 minutes, depending on size of pieces. Drain and cool.

Pack pears and cover with cold 40 percent syrup. For a better product, add 3/4 teaspoon (2250 mg) ascorbic acid to a quart of cold syrup. Leave headspace. Place a small piece of crumpled water-resistant paper on top to hold the fruit down. Seal and freeze.