$printer->printFile($fh, 'jobx')

The documentation says that printFile wants a filename, not a handle. An in-memory file like this one does not have a filename. You probably want to use File::Temp instead (more examples):

use File::Temp qw/tempfile/;

my ($tfh,$tfn) = tempfile(UNLINK=>1);
print $tfh "Some Data...\n";
close $tfh;

$printer->printFile($tfn, 'jobx')
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Update: And as I mentioned here, you can use the DIR parameter, and as others have mentioned, you can point that at a RAM disk or similar file system.