Make perl think your header is one line:

my $header;
{
    local $/ = 'END';
    open FH, "< $filename" or die $!;
    $header = <FH>;
    close FH or die $!;
}
[download]

Localizing $/ in brackets cuts out bad side effects, and just reading to the marker gives you minimal read length.

After Compline,
Zaxo