I actually replied to this yesterady but got busy and didn't get past the preview page.

All good information. The %ENV hash I totally overlooked. I remember reading it a year or so ago in Learning Perl and thinking "I won't need that for a while." I was right, but now that I needed it...

For the record, a simple...

my $display = $ARGV[0];
$ENV{'DISPLAY'} = $display . ":0.0";
[download]

...worked just fine.