Adding another bit:

if (1) {
   $_= <<"   END";
   Here is some
   text which needs
     to be flush to the
     left margin
   and has indented parts
   END
   /^(\s*)/;
   print s/^$1//gmr;
}
[download]

Update:
Here is another one:

if (1) {
    print <<"    EOT" =~ s/^(\s*)//r =~ s/^$1//gmr;
    Here is some
    text which needs
        to be flush to the
        left margin
    and has indented parts
    EOT
}
[download]