Cascading customConfig settings

I have editors on multiple pages on my site, many with different settings, such as toolbars. What I was hoping to do is have all my common settings in one configuration file and then have settings for each type of editor stored in individual config files. I don't want to specify setting in-page, since several instances will have exactly the same settings.

I tried putting multiple toolbar definitions in the global config.js:

CKEDITOR.editorConfig = function( config ) {
  config.toolbar_Bar1 = [ [ 'Cut'] ];
  config.toolbar_Bar2 = [ [ 'Copy'] ];
  config.toolbar_Bar3 = [ [ 'Paste'] ];
};

Then I have a custom config file called instance1.js which looks like:

CKEDITOR.editorConfig = function( config ) {
  config.toolbar = 'Bar1';   
};

Then in my page, I do this:

CKEDITOR.replace( 'EditorArea',
{
  customConfig : 'instance1.js'                  
});

When I do this, I get the error:
"u is undefined" at line 66 of ckeditor.js

If I remove the following from instance1.js the error goes away:

config.toolbar = 'Bar1';

It seems that as soon as I specify a custom config in-page, the settings in the global config.js are completely ignored, instead of cascaded.

I also tried putting all of the toolbar settings in baseConfig.js and changing my instance1.js to:

CKEDITOR.editorConfig = function( config ) {
  config.customConfig = "baseConfig.js";
  config.toolbar = 'Bar1';   
};

It seems like this just completely ignores the second line where I set the toolbar.

Can someone tell me what I am missing here? Or is there no way to actually cascade settings, and I need to duplicate all my common settings in all of my custom config files? Thanks.