Yes. It's very easy to do. Simply create another directory in the root of the DVD and name it EXTRAS. Place all the non-DVD content in that directory.

The full version of DVD Architect can do this for you. I don't know if DVDA-Studio has this function built in, but even if it does, i find it rather limited. It requires that you already have that directory set up on your hard drive containing everything you want in it, and nothing else. For this sort of thing i'll usually uses DVDA only for preparing the DVD. Then i'll burn with Nero, which has a lot more robust features for setting up the DVD directories.