This utility takes a dvips-generated postscript file, and creates a new potscript that has two of the pages of that on each new page. It only works for the output of dvips; for a4 paper only (because some magic numbers like 421.37259980 are hard-coded), and it can not put more than two pages on one page. It's ugly, but it works.

I tried to do this as a shell script first, but that attempt failed miserably.

#!/usr/bin/env perl
# creates a two-paged postscript file -- works for dvips-generated fil
+es only
# assumes a4 paper

use warnings;
use strict;

my $duper;

sub main {
    @ARGV or
        die "usage: psdup foo.ps";
    for my $arg (@ARGV) {
        $arg =~ /(.*)\.ps|(.*)/s or die "internal";
        my $prefix = $+;
        my $ifile = -e $arg ? $arg : -e $prefix . ".ps" ? $prefix . ".
+ps" : 
            die "cannot find file: $arg";
        open my $I, "<", $ifile or
            die "error opening file: $ifile";
        my $tfile = $prefix . ".duptmp.ps";
        my $ofile = $prefix . ".dup.ps";
        open my $O, ">", $tfile or
            die "cannot open temporary file $tfile";
        my $s = 2;
        $! = 0;
        while (defined(my $l = <$I>)) {
            $s and do {
                2 == $s and
                    $l =~ /^%%Creator: dvips\b/ and
                    $s = 1;
                1 == $s and 
                    $l =~ /^%!$/ and
                    do {
                        print $O $duper or
                            die "error writing file $tfile: $!";
                        $s = 0;
                    };
            };
            print $O $l or
                die "error writing file $tfile: $!";
        }
        $! and !$!{"EBADF"} and
            die "error reading file $ifile: $!";
        $s and
            die "$ifile is not dvips-generated postscript";
        close $O or
            die "error closing file $tfile: $!";
        system "ps2ps", $tfile, $ofile and
            die "ps2ps failed";
        unlink $tfile or
            die "cannot unlink $tfile: $!";
    }
}

$duper = <<'EOP';
%ambrus duper

/zbd { bind def } bind def
/z-showpage { showpage } zbd
/z-scale0 { 
    gsave 0 421.37259980 translate 
    0.70710678 0.70710678 scale -90.0 rotate  
    } zbd
/z-scale1 { 
    gsave 0 842.7451996 translate 
    0.70710678 0.70710678 scale -90.0 rotate  
    } zbd
/z-unscale { grestore } zbd
/z-dupe-odd false def
/z-flush { z-dupe-odd { z-showpage } if } zbd
/bop-hook { 
    z-dupe-odd { z-scale0 } { z-scale1 } ifelse 
    /z-dupe-odd z-dupe-odd not def 
    } zbd
/eop-hook { z-unscale z-dupe-odd not { showpage } if } zbd
/end-hook { /z-flush } zbd
/showpage { } zbd

%
EOP

main;

__END__
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