Merge Directories virtually (not copying)

I want to merge all my movie folders together.
I got the ~/Movies with some stuff but not too much because it is still on the SSD.
And I have a /Volumes/HFSData/Movies with all the kind of archived movies.

I would like something like Windows 7 libraries that simply lets me merge the files of different folders in one directory without the files actually being there (physically).
The HFSData HDD partition is only mounted when I launch a script but if it is I would like the linked files or folders to show up.

Thing is I can create an ln -s link but that is effectively nothing else than an alias in Windows. I deactivated spotlight on the HDD because it doesn't let my HDD sleep and if spotlight indexing would only find the links it would be perfect.
I just cannot figure out how to link the contents of a folder as a whole into another folder (~/Movies/).

I know about Spotlight smart searches but they always find too much and small stuff I don't want there. I just want to specify the folders that show its content there like the virtual libraries Windows offers.

Any ideas, suggestions??

 

Not exactly very convenient I was hoping for something simple to use.
It would require some kind of script to create those links automatically.

I ended up splitting up the HDD Movies Folder into many small folders and linked some of those. That works quite good too. Although it would be cool if the links hide automatically if the file is not mounted.
Would be require some script again. I guess I will just live with this setup.