[mod_python] handling virtual files

Hi, i need some directions :-)

i need to have 'virtual' and real files on a tree, virtual paths have a 
folder on the root which somehow gets the next folder, and again and 
again. mixing different methods. /dir1/dir2/dir3/dir4/file

dir1 is simply a folder, dir2 is 'mounted' for a database, where dir3 is 
  simply a folder, and dir4 is a 'COW' (copy on write) of another directory.

i get the file into temporal location and now i call the file handler 
over the temporal location but thinking its on the virtual one.

but req.filename is read-only.. how should i solve this problem? what do 
you recommend?

TIA,
Alejandro Mery