Actually - the more I think about this.
the hack.inc.php file (or extras.inc.php file) doesn't need any includes.
It can just be like this:
<?
$config['game_table_width'] = 'whatever';
$config['game_cell_padding'] = 'thisthat';
?>
It only need to contain the variables.
Then, rather than having to modify any threads scripts with extra includes.
The include statement could be added right into main.inc.php - which is a script which never gets overwritten with upgrades.
Then you could include the misc config variables into threads, without having to modify anything extra.
We could release it as a "mod" then any mods we write could state in the instructions that it required the hack.inc.php mod. Thus eventually - everyone who runs several mods will add this once, and be able to use it for all settings for mods today and in the future.