Normally I try to upload screenshots to Commons, but it's kind of a pain in the butt to upload MediaWiki screenshots there because you have use custom licensing templates every time. So if you just want to upload locally to MediaWiki.org like S was doing I think that works. We also considered just opening a Dropbox folder, since this stuff doesn't necessarily need to be permanent.
Please don't just use dropbox. Transparency and all...
I don't understand why mediawiki.org would be easier to upload than commons. Just use https://commons.wikimedia.org/wiki/Special:Upload instead of uploadwizard and put your custom license tag in the permissions field (and have the license drop down set to none).
--bawolff