Cubase Pro 8 installation

I have successfully installed 8 on Windows 8.1 and am now installing it on Windows 7 sp1 (I have both Windows dual booted on the same PC) but don’t have enough space on my C drive to install the Groove Agent Content (apparently you need 3gb).

Is it possible to install this content on a separate partition - the installer seems to insist otherwise! If not, why not?