Actually, ezjscore can use JSMin::minify (when Packer=3 is used), but several other packers for JS exist (the most famous are yahoo compressor, dojo shrinksafe), and even for CSS

=> It would be nice to indicate which packer to use for css or/and for js, when Packer=3

Why not something in ezjscore.ini, like (and let the user choose the packer engine he/she wants)
[eZJSCore]
#JavascriptPackerEngine=jsmin
JavascriptPackerEngine=yui-compressor
#JavascriptPackerEngine=dojo-shrinksafe

#StylesheetPackerEngine=ez-default (the default packer that exists in ezjscPacker::optimizeCSS())
StylesheetPackerEngine=yui-compressor
#StylesheetPackerEngine=dojo-shrinksafe

Here is the way to use YUI compressor:
http://developer.yahoo.com/yui/compressor/#using
A php class that wraps the call of yui compressor, for inspiration for eZJScore:
http://code.google.com/p/minify/source/browse/trunk/min/lib/Minify/YUICompressor.php

Dojo shrinksafe:
http://shrinksafe.dojotoolkit.org/

And as shrinksafe is also a .jar, just like yui compressor, the same link above (YUICompressor.php) could be, with slight modifications, a wrapper for using shrinksafe from php static function ezjscPacker::optimizeScript()