my $nextIpIndex = 0;
my @ips = ('xxx.xx.xx.xx', 'xxx.xx.xx.xx', 'xxx.xx.xx.xx', 'xxx.xx.xx.xx');

sub callBeforeRequest
{
  @LWP::Protocol::http::EXTRA_SOCK_OPTS = ( LocalAddr => @ips[$nextIpIndex] );
  if( (++$nextIpIndex) >= @ips ) { $nextIpIndex = 0; }
}