Please change the url of the upload link in the toolbox, so set the following line under wgUploadNavigationUrl:
'incubatorwiki' => 'http://incubator.wikimedia.org/wiki/Incubator:Upload',
That way it goes to [[incubator:Incubator:Upload]], a page containing more information how to upload on Commons (locally disabled for non-bureaucrats), otherwise they see only a sentence "restricted to bureaucrats".
I started a talk on http://incubator.wikimedia.org/wiki/Incubator:Community_Portal#Upload_page but, as we're a small community, no one reacted. And this does not really needs a community consensus.