$config = {
 verbosity => 3,
 logger => new Logger(),
 ...
 # hundreds of configuration settings
};

##</code><code>##

$params = {
  from => ...,
  to => ...,
  # override the timeout of the system-wide config
  timeout => ...,
  # this is the config read from file
  config => {
    verbosity => 3,
    logger => ...,
    timeout => 5,
    ...
  }
};
sub distance {
  my $params = shift;
  # the timeout value will be the config's unless
  # caller passed their own value to temporarily override it
  my $timeout = exists($params->{timeout})
    ? $params->{timeout}
    : $params->{config}->{timeout}
  ;
  ...
  # similarly, I return back multiple values in a hash(ref)
  return {
   errormsg => 'nothing',
   status => 1, # all OK!
   distance => 42
  };
}
# call it
my $ret = distance($params);
die $ret->{errormsg} unless $ret->{status} == 1;

##</code><code>##

# I am skipping some boilerplate
package Calc;
sub new {
  my ($configfile, ...) = @_;
  my $config = read_configfile($configfile);
  my $internal_data = {
    config => $config,
    stash => {}
  };
  # bless etc.
}
sub distance {
  my ($internal_data, $params) = @_;
  # internal_data holds config,
  # $params holds from, to and anything to override
  # config just for the life of this call
  ...
  # optionally save results to the stash
  $internal_data->{stash}->{distance} = 42;
  # return something back
  return {
   errormsg => 'nothing',
   status => 1, # correct
   distance => 42
  };
}

##</code><code>##

my $calcobj = Calc->new('settings.config');
my $res = $calcobj->distance({
  from => ...,
  to => ...,
  # optionally temporarily
  # override system-wide config setting
  timeout => ...,
});