This may be of interest to some people.  I was poking around in the CC-BY and CC-BY-SA 2.0 legal code, and there's an important clause covering adaptations (that is, derivative works) that works in OGA's favor:

4(b). You may distribute, publicly display, publicly perform, or publicly digitally perform a Derivative Work only under the terms of this License, a later version of this License with the same License Elements as this License, or a Creative Commons iCommons license that contains the same License Elements as this License (e.g. Attribution-ShareAlike 2.0 Japan). [...] (emphasis mine)

What this means to us is that, while we can't accept CC 2.0 works on their own (due to incompatibilities with libre software), it's possible to create derivative works of those works and license them under the 3.0 licenses.  What this means is that, for example, you can grab CC-BY 2.0 photos off of Flickr (seriously, wtf, I thought they supported the 3.0 licenses the last time I looked.  Maybe I'm going crazy...), transform them into tiling textures, and release those textures under CC-BY 3.0 (or later) -- the same goes for CC-BY-SA 2.0 -> 3.0.  The important caveat is that you must transform the work in some way.  If you just post the original work, that's not a derivative, and you're not allowed to just update the license without permission from the author.