If your Lappy has two HDD/SSD, then you can install WIN 7 on the other one. If it has the space for two then you can buy a HDD/SSD and can install WIN 7 on it. Unplug the drive with WIN 8, when installing WIN 7.
If you have only one HDD/SSD, then unfortunately you have to format the WIN 8 installation. When the drive is empty first install WIN 7 then WIN 8 on it.
Good luck.