How to add custom button on toolbar using API only ?

Hi,

I have create one custom toolbar in config.js.

config.toolbar_message_center =
   [
      { name: 'document',    items : [ 'Source' ] } ,
      { name: 'basicstyles', items : [ 'Bold','Italic','Underline','Strike'] },
      { name: 'colors',      items : [ 'TextColor','BGColor' ] },
      { name: 'links',       items : [ 'Link','Unlink'] },
      { name: 'paragraph',   items : [ 'NumberedList','BulletedList' },
      { name: 'tools',       items : [ 'Maximize' ] }
   ];

I have used this toolbar lot of places, but now i required new toolbar which same as above only need to add one more custom button,

its possible but for that i need to create new toolbar with diff. name in config.js.

config.toolbar_message_center_2 =
   [
      { name: 'document',    items : [ 'Source' ] } ,
      { name: 'basicstyles', items : [ 'Bold','Italic','Underline','Strike'] },
      { name: 'colors',      items : [ 'TextColor','BGColor' ] },
      { name: 'links',       items : [ 'Link','Unlink'] },
      { name: 'paragraph',   items : [ 'NumberedList','BulletedList' },
      { name: 'tools',       items : [ 'Maximize' ] },
      { name: 'custom',      items : [ 'MyButton' ] }
   ];

Is any way to add new button using API without changing in old toolbar definition or way to extend existing toolbar using API.

Thanks