How about:

package BitStream;

use constant BUF_SIZE => 2048;
use POSIX qw(ceil);

sub new {
  die "Correct usage is BitStream->new(filename)" unless @_ == 2;
  my ($class,$filename) = @_;
  
  open my $fh,"<",$filename or die "Couldn't open $filename: $!";
  
  read($fh,my $buffer,BUF_SIZE);
  
  my $self = { fh => $fh, buffer => $buffer, dead_start => 0 };
  
  bless $self,$class;
}

sub get_bits {
  my ($self,$bits) = @_;
  no warnings "once";
  return "" unless $bits+=0;
  
  # ok, make the buffer big enough to handle the request
  my $buf;
  $self->{'buffer'} .= $buf while length($self->{'buffer'}) * 8 + $sel
+f->{'dead_start'} < $bits && read($self->{'fh'},$buf,BUF_SIZE);
  # figure out our end position within the buffer
  my $bytes = ceil(($bits + $self->{'dead_start'})/8);
  my $return_buf = unpack("B*",substr($self->{'buffer'},0,$bytes));
  $return_buf = substr($return_buf,$self->{'dead_start'},$bits) unless
+ $return_buf eq "";
  $self->{'dead_start'} = ($bits + $self->{'dead_start'}) % 8;
  $bytes-- if $self->{'dead_start'};
  substr($self->{'buffer'},0,$bytes) = "";
  return $return_buf;
}

"Give me liberty or at least the remote";
[download]

Of course, I must admit that I prefer bit twiddling over this.