Custom Configurations in PHP created editor

I have been pounding my head on this.
Please, how do I call a custom configurations file in a PHP created editor

The tree structure is as follows:
root/update/fckeditor/

the test.php and custconfig.js files are in the root/update/ directory.

I can retrieve the custom config in the root/update/fckeditor/fckconfig.js file by setting value:
FCKConfig.CustomConfigurationsPath = '/update/custconfig.js' ;

But I have been unable to call the root/update/custconfig.js from the root/update/test.php create editor file

test.php code

$oFCKeditor = new FCKeditor('FCKeditor1') ;
$oFCKeditor->BasePath   = '/update/fckeditor/' ;
$oFCKeditor->CustomConfigurationsPath = '/custconfig.js'  ;
$oFCKeditor->Value      = 'blah blah' ;
$oFCKeditor->Create() ;

I have also tried
$oFCKeditor->CustomConfigurationsPath = '/update/custconfig.js' ;
and variations of slash in front, no slash in front, ../custconfig.js, and so on.

And I manually clear the cache to make sure edited .js are loaded.

What am I doing wrong?
Thanks much.