Add the pears and ginger to a large pitcher. Cut three slices out of the middle of the lemon. Place the ends of the lemon in a zipper bag or airtight container and place in the refrigerator; you'll use those pieces to garnish the rims of the glasses later on. Stick three cloves into the flesh of each lemon slice and add to the pitcher.
Pour the wine, rum, and brandy over the fruit in the pitcher. Seal tightly or cover with plastic wrap and refrigerate for at least 4 hours, up to 8.
Have your glasses washed and ready. Place the sugar and ground ginger in a small bowl and mix together with a fork. Pour sugar mixture into a small saucer and spread it to the edges. Wet the rims of the glasses with lemon juice by dragging the cut sides of the lemon ends around the rims of the glasses, then invert the glasses into the sugar, pushing and turning until coated. Turn glasses right side up and set aside.
Strain the sangria mixture through a sieve and into a second large pitcher. Add the pear slices back into the pitcher and the lemon slices if desired; discard ginger slices and any other sediment.
Add a few slices of pears to each glass, then fill halfway with sangria mixture. Fill the rest of the way with ginger beer. Add straws, if desired, and serve.