With some experimenting I came up with this recipe:
Homemade Borage-Flavored Lemonade
Ingredients - flavored sugar syrup:
1 cup sugar
1 cup water
1 cup lemon juice (juice of about 4 to 6 lemons, 5-10 lemons for 2 cups juice)
3 to 4 medium-sized fresh, washed borage leaves (other flavoring ingredients can also be used: Lavender, Basil, Mint, Vanilla, Nasturtium or other herbs, each at different times)
In a small saucepan heat the sugar and water to boiling and until the sugar is dissolved completely. Boil it for a couple of minutes more to thicken. Remove from heat and add flavoring ingredient, in my recipe I used fresh borage leaves from my garden and allow to steep about 10 minutes until sugar syrup is cool, then strain out the borage leaves.
While sugar syrup is cooling, use a juicer to extract the juice from 4 to 6 lemons or enough for one cup of fresh juice. Add the juice and the sugar syrup to a pitcher. Add 3 to 4 cups of cold water, more or less to the desired strength and taste. Refrigerate 30 to 40 minutes. Serve with ice, sliced lemons, and if desired, garnish with Borage leaf. Too sweet or too sour can be adjust to taste by adding more sugar syrup or water.
Caution: Sugar syrup gets extremely hot and can cause terrible burns!
Some information about sugar syrup.