### i know this does not work, i am showing the idea
my $ftp = Net::FTP->new($server,$user,$pass);
$ftp->cwd("/some/dir");
pipe(R,W);
$ftp->put(\*R,'filename');
print W "data here\n";
$ftp->quit;

##</code><code>##

pipe(READ,WRITE);
$pid = fork();
if ($pid == 0) {
    ## child (read)
    close(WRITE);
    $ftp->cwd("/some/dir");
    $ftp->put(\*READ,'filename');
    $ftp->quit;
} else {
    ## parent (write)
    close(READ);
    ## ... do some cool processing for $data
    print WRITE $data;
    close(WRITE);
}