printing duplex with -o

[Linda Hanigan]

All of my programs create pcl and hp-gl. I am currently working on converting them to generate postscript. The machine I use for development has a HP laserjet 1320 and the production machines use a HP laserjet 4250. On the 1320 I can use lpr -o sides=two-sided-long-edge to turn on duplex, it is off by default. However the HP laserjet 4250 ignores the duplex option. If you turn on duplex as the default then it prints everything duplex otherwise nothing is duplex. Using pcl I can control duplex within the file. Any ideas on how to control if a file prints duplex on the 4250 when printing postscript files. I started the project because it allows the user to easily produce a pdf file to email by having the program use ps2pdf. However I really like the ease of using the x and y values to check page boundaries etc.
Any suggestions would be greatly appreciated.
          Linda