You can specify a virtual file handler for a filename record using the /ap option:
fs /d dbase.ref /f filename /ap program-name
where program-name specifies the virtual file handler that the Fileshare Server calls to process all I/O requests on the data file. See the section Virtual File Handler in the chapter, Advanced Operation.
The filename definition in the /f entry (corresponding to an /ap entry) can include a trailing wildcard to specify that groups of files are to have their requests passed to the specified virtual file handler.