I jumped to delusions.
Maybe that would work. Something else that might work is to spool the .iso off and make a bootable flash drive. Before you try this, you might want to plug in a flash drive, then see if the laptop sees it from the BIOS as another drive. Older laptops may not.
Something else else that might work if you have a second (empty) external drive:
use your .iso writing program to write the image to that drive, making it bootable. Then install Win7 from that drive.