I keep Vista on my Windows 7 USB install stick which is also my tool kit with several dozen installers on it. When I need to install Vista, I sweep the Windows 7 install files into their folder for storage and spill the Vista files out into the root of the stick.
The stick was originally set up by writing Windows 7 installation ISO to it using Universal USB Installer
with Windows 7 in the dropdown menu. I then copied in the other tools and Vista extracted ISO in its folder.
As stated whichever OS you're needing to install must have its files spilled out into the root to boot.
Why would you want to take Windows 7's branding off of the installation process?