You need to enable the custom index, and override its view in your theme by creating a folder called mod/yourtheme/views/default/canvas/layout/new_index.php. Place your theme under the custom_index plugin then.

Okay, you lost me completely. But let me play a bit and I'll come back with more questions.

@Ed - try following this page in the Elgg documentation: http://docs.elgg.org/wiki/Overriding_a_view

Copy the view php file from your theme rather than from the core. Put the plugin after your theme. In the view file, add something like this:

<div id="sub_toolbar">

        My new toolbar

</div>