Restrict non-administrators to their own images

I'm using Image-Assist with TinyMCE and would like to remove the All-Images option from the pop up window, so that users can only select their own images. Is there a switch for this somewhere?

I found this in the Image-Assist module...

$images_link = $image_add . l(t('my images'), $dir, null, "user=$user->uid"). ' | '. l(t('all images'), $dir);

...which creates the menu.

What I would like to do is drop the 'all images' option if the user is not the member of a particular group i.e. they are not administrators.