Bootcamp: Windows installer couldn't find drivers. I placed them on the installer USB. Where should they go? I have a Late-2013 model 15 inch rMBP, with El Capitan. I downloaded a Windows 7 64bit ISO from Microsoft. 

Opened up Bootcamp Assistant, created a bootable Flash drive, and downloaded the Windows Bootcamp Support Files from Apple. 

I extracted the zip, and copied the files over to the Bootcamp USB drive.

Back in Bootcamp Assistant, chose "install windows" option, created my partition (100gb), it seemed to be zipping along then it restarted my laptop and booted into the windows installer.

Windows installer stated that it could not find the necessary drivers, and to insert the disc containing them. There was an option to select folders on the hard drive which contain the files, but it said it could not find them in any of the folders. 

So.. what did I do wrong? Where should the support files be extracted to? Does it need to be an entirely separate USB from the Windows 7 USB? ugh. Not sure why this isn't working.
Just following up. I unmounted the .ISO file, deleted the windows partition and re-created the USB drive... Seems to have worked this time. Gonna chalk the issue up to an anomaly.

Like @DavidAnderson pointed out in the question comments, users with a Retina MacBook Pro 15 inch should use This version of the support software, not the one I linked in the original question.

Cheers.