...
use XML::Simple qw(:strict);
use IO::File;
use Carp;
...
my $XMLHandle = IO::File->new($xmlfile, O_RDONLY) or ...

foreach my $Account (keys %Accounts) {
  # get an in-memory hash representation of the fragment
  my $xml = LoadAccount($Account);

  # process the in-memory hash of this fragment
  # your code goes here
  ...
}

sub LoadAccount {
  my ($Account) = @_;

  my $length = $Accounts{$Account}->{End} -
               $Accounts{$Account}->{Start};
 
    my $xml;
    # I have removed all error handling of the read
    # and seek to simplify this example 
 
    # Jump to the required offset in the file
    $XMLHandle->seek($Accounts{$Account}->{Start}, SEEK_SET);

    $XMLHandle->read($xml, $length); 

    eval {
        # parse the XML, using XML::Simple to get the resulting data
        # structure the way you like it
        $xs = XMLin($xml,
               ForceArray => [qw(...)],
               KeyAttr    => []);
    };
 
    if ($@) {
        $croak("Account $Account :: cannot parse xml $xml - $@");
    }
 
    return $xs;
}