Htmlizer : custom helpers

[item]

Hello,
is possible to create a custom helper for htmlizer ? include path maybe in upgrade safe ?

Htmlizer.php
line : 239
sample :

'secondsToHHmm' => function ($context, $options) {
       $hours = floor($context[0] / 3600);
       $minutes = floor(($context[0] / 60) % 60);
       return $hours .',' .$minutes;
} 

If a custom include path exist, that will be very cool !
Here a possible function that will be useful :

http://jsfiddle.net/mpetrovich/wMmHS/

this will be great if we can add like custom "formula".. without extend pdf entrypoint and htmlizer and pdf service.

Cheers