Yes, you can install apps from the CS6 Design Standard separately.
Insert the disc, during installation process, choose the apps that you need installed and proceed with installation.
Bear in mind that most apps use 'common files' which will be installed one-time (either if you install all apps or even just one and if that one app requires those common files).
8.5Gig is really not that much if you ask me! What is your hard drive capacity? Are you sure your computer meets the minimum requirements to run all Design Standard Apps?
I am concerned about the 8.5 GB of storage needed.
In these days of terabyte drives, you'll run out of space very quickly if you're struggling with 8.5GB to install the apps themselves.
Agree with John. If you're already concerned about actually installing the apps, then working with them isn't going to be much fun on your system...