In a cocktail shaker, add the lemon slices and desired amount of ginger slices, depending on how spicy you enjoy your drinks. Muddle or crush the lemon slices and fresh ginger together. Fill the shaker with ice and add the vodka and agave syrup. Shake to mix the ingredients together. Add the pale ale. To combine, gently transfer the mixture back and forth between each cup of the shaker. You dont want to shake with the beer because of the carbonation. Strain into a cocktail glass and enjoy.