I’ve got some idea’s of how to do this on the PC side, but are OS dependant
Linux, you can use aufs or unionfs
and a nifty trick in ubuntu 13.04 to default kernel supports nfs export of merged directories
in windows there’s some advanced drive options for mounting, probably not exactly what you want
but example
parent folder - contains folder1 and folder2
folder1 and folder would represent actual drives mounted inside the parent folder
these would not be shortcuts, etc …
it would actually be hard mounted
ie you share out the parent folder only
and everything below it would be shared as well
besides there I think there’s some software that can do this in windows, like drive blender, etc …
edit. re-reading your post
if you’re talking about drives being shared by the hub
media library is your best bet
Playing with WDLXTV I did try some of this for a while
unionfs works, but dmaosd is very picky about where you mount things, and how they are mounted
linux symlinks also don’t work on ntfs or fat32 drives
but creating the symlinks would also require cmd line access,
I got a play list system to work once, but it had some draw backs as well
you have to log into network shares first
then go to local media where the playlist would be stored
but it did work without any cmd line access and since all your media is attached locally to wd hub, it might work
you’ll still be able to see the single folders, but you’ll have a merged playlist you can choose and browse