dissociate MyDocument and odb default path

Hi all

is it possible to have different paths for the "My Documents" setting 
and the default directory where OOo creates .odb files

the problem is that i want to specify the MyDocument on a shared path 
over a network for multiple users (for any "Open" operation, default 
path, written protected) but i also want that any mail merge ressource 
(.odb files cretaed from a calc file for example) is stored on a per 
user basis to avoid conflicts and have written permissions

seems to be located in paths.xcu file but i don't find any information 
on the keys that may be used in this file
i may be wrong on digging on this file though

Thanks in advance

Laurent