Also take a look in the manual at combining file_load() and then add_buffer().
Ive never used it but it may help, if it works the way I think it does.
File_Load() loads the file from WRS into memory space (not extract to the hard disk),
and add_buffer() puts the memorised file into the 3DGS virtual file system, so any
file_open type function can access.
Theoretically...