Josh, from a web page there isn't much you can do (that I know of) to influence the printer settings. All I can do from the server side is generate the PDF suitable for printing on envelopes. From there I hand it off to the user to hit print and get it directed to the right tray. If you really need full control of the print job I think you would need to write a native app on the client side, or maybe a Java applet if you get the permissions right....but I'm not a Java person so take that bit with a grain of salt.