The [Share-Alike license](http://creativecommons.org/licenses/by-sa/3.0/us/) says:
*Any of the above conditions can be waived if you get permission from the copyright holder.*
So if you're the creator, you could presumably waive any restriction on how you use the material. The clause in the SO legalese may be there because content you created may have been edited by others, in which case you're no longer the only one who has an interest in the material.