You can still install Windows 7. What you will need to do is create a USB drive with the drivers separately from the Bootcamp program as it will no longer fetch the correct drivers for your version of Windows. Installation of Windows 7 is essentially the same as Windows 8 or 10, even though the app does not prompt you for Windows 7. Refer to the following support articles from Apple.
https://support.apple.com/en-us/HT205016
https://support.apple.com/kb/DL1720?locale=en_US
Download the drivers in the second link and burn to thumb drive. Install Windows and once you are on your desktop in Windows, open the thumb drive and run setup. It will install the proper drivers for your model of Macbook. Once you have finished this process, I strongly encourage you to visit Intel's website and download the latest driver for your HD 4000. Apple does not provide the newest Intel drivers and the patch from Intel will improve software support.