One method is to create a pipe on unix that performs a specific task, say printing in your case. The following example shows a pipe that is created such that it compresses that file being written to (in this case, PL/SQL).
#--Setup the pipeline to be used in the export process
mknod $dmp_file_name p
compress < $dmp_file_name > $dmp_file_name.Z &
You should be able to formulate a pipe to send the contents to a printer.
Or, you could set up a cron job to look at files being generated and once completed, send it off to the printer.