I tried to compare binary strings which encode "equality tables", halves (triangles). I generate these strings through eval-group inside the regex:

#!/usr/bin/perl -l

use warnings;
use strict;

my $template = 'neocene';

my $equality_triangle_template = '';
$template =~ m/(.).*?(.)(?{ $equality_triangle_template .= $1 eq $2 ? 
+1 : 0 })(*FAIL)/;

my @dict;
@dict = <>; # <-- 354984si.ngl
chomp @dict;

my @good = grep {
    my $equality_triangle_word = '';
    m/(.).*?(.)(?{ $equality_triangle_word .= $1 eq $2 ? 1 : 0 })(*FAI
+L)/;
    $equality_triangle_word eq $equality_triangle_template;
    }
    grep length == length $template, 
    @dict;

print for @good;
^Z
kaitaka
lauhala
metreme
neocene
tempete
[download]

P.S.One can use (.).*(.) instead of (.).*?(.), omitting question mark - non-greediness modifier (possibly it is only slightly faster).