I do not believe there is a way to get the free upgrade without actually updating. There are a couple of alternatives though.
1. He could upgrade to Windows 10, make sure it is activated, and then use the revert function to restore Windows 7. Reverting has been problematic for some, so this is not a fail-safe solution.
2. This solution is safer, but you need access to the applicable program and another PC. Your friend could use imaging software to make a complete backup clone of his hard drive before upgrading to Windows 10. He would then upgrade, and after Windows 10 is activated he would restore the backup image. This is what I did. I work in IT, and our PC repair department has high quality imaging software. I used that on my own. I was planning to use Windows 10, but my laptop is older and it had too many driver issues. I restored my Windows 8.1 image, and I have been using that ever since. I wouldn't be surprised if the driver problems have been resolved by now, but since I probably won't be using it much longer (due to its age) I decided to keep it on Windows 8.1.