for (grep /^default_option_/, keys %def) {
   my (undef, $option) = split /_/, $_, 2;
   $s{$option} = $def{$_};
}

##</code><code>##

my @keys        = grep /^default_option_/, keys %def;
my @short_keys  = map +(split /_/, $_, 2)[1], @keys;
@s{@short_keys} = @def{@keys};