Most car auto-stores sell Turtle Wax coloured wax that comes with a wax crayon. Buy the one that most closely matches the colour of your car to fill in the stone chips, and polish using the coloured wax a few days before the car needs to go back. If you are lucky, then the stone chips will be barely visible. The wax will wash out with a few washes though, hence doing it just before the car needs to be returned.
If you spend time and money getting them fixed permanently just now, sods law dictates you will get a few more new ones to take there place within days.