Unionfilesystem plugin: how to control drive balancing

I've installed the new unionfilesystem plugin, but I'm looking to a way to keep some control on how the drives are used/allocated (from a usage balancing point of view).
When I was using the aufs plugin there was a checkbox (mfs) that if checked was forcing the drives' balancing, while if unchecked was preserving the folder structure.
I had this box unchecked and if I remember correctly how the system was behaving, if I had one folder (XYZ) created only in few disks out of the pool, the moment i was going to create (via aufs filesystem) a new file/folder in XYZ, this was going to be stored only in these few disks.
Now, with the unionfilesystem, when I do the same and I create a new file/folder in XYZ, a new folder is eventually created in one of the other disks (part of the same pool, but with more free space) and the file/folder stored in there.
Which I assume is because the underlying aufs is automatically configured as if mfs is checked.

This is good from a disk balancing point of view, but it is mixing up all different type of files (pictures, music, movies, ...) for which I would still like to have some control/segregation on which disks they are stored (while having only one single entry-point for the media-player application).
(just for clarity: I use only the poolshare filesystem in samba to read, write files, while I'm creating these "predifined subfolder structure" directly from the CL)

is there a way to still keep some control on the disk space allocation (preserving the folder structure) also with the new plugin?
(may be manually editing some configuration file?)

thanks.

If i remember right (!), the "risk" to have a folder created in another drive was only at the moment the drive(s) with the already created folder was almost full. But if there was still a reasonable amount of space in this dive(s) the new folder was going to be created here and not in the other drive (even if it was eventually with more free space). And this was perfect (at least for the way I was trying to manage my files): it was "trying" to preserve the structure as much as possible (up to the moment there was a risk of running out of space).

Anyway I will look into symlinks (not sure I can do what I want, but will give it a try...).

Just a final question: as it takes few seconds to create a pool with the unionfilesystem plugin, will it be OK if I delete the pool every time i want to do some manual housekeeping (move/group files/folders on specific disks) and than recreate the pool right after? I guess it should be OK this way, but just to be sure.

thanks again.