Another Approach

One suggestion was to create file called tray.ps, as below, and cat it at the printer immediately before the file you want printed:

    cat tray.ps my_file.ps | lp

    %!PS-Adobe-2.0
    %%Title:  tray.ps 
    %%CreationDate: May 10 17:34:49 MST 1996  
    %%EndComments

    % Use this file to verify that the PostScript printer can pull
    % a page from any installed tray in a multiple tray printer.
    % For the LaserJet 4, trays are as follows:
    %  tray 0 = upper cassette
    %  tray 1 = lower cassette (optional high-capacity tray)
    %  tray 2 = envelope feeder (if installed)
    %  tray 3 = multipurpose tray
    % For the DEC Print Server 17:  1 setpapertray % upper cassette
    statusdict begin
      1 setpapertray    % upper cassette 
    % 0 setpapertray    % lower cassette
    end