As others have pointed out, this is because Net::FTP is calling fileno. I just tried this and it worked for me - I don't think it will solve all your problems, but it might be a good starting point.

my $data="FOOBAR";

pipe PIPEREAD, PIPEWRITE;
print PIPEWRITE $data;
close PIPEWRITE;

my($ftp) = Net::FTP->new($destserv) || die "error connecting\n";
$ftp->login($destuser, $destpass);
$ftp->binary();
$ftp->put(*PIPEREAD,"remotelogfile") or die "error uploading\n";
$ftp->quit();
[download]

Basically, I used pipe to create a real pipe between Perl and whatever Net::FTP is doing.

Have fun,

Rich