Cut lemon into tiny wedges that will fit into 1 cube of an ice cube tray. Place one wedge into each cube, cover with water and freeze.
Thaw concentrated grape juice and fruit punch; mix together. Set aside in refrigerator.
Just before serving, mix a third of the concentrate with a third of the soda. (I like to make in batches of three so it stays bubbly and fresh during the event). Pour the soda in slowly. Add a tray of the lemon wedge ice cubes and a few generous scoops of raspberry sorbet.