So... I was able to use debian experimental PPA (using /opt/debextra, for those who are wondering how I did it) to make an updated libc6 sce. But I can't load it, as it claims that it's already installed, so...
How to force sce-load? I really need the update to work so I can get compton working. (It needs glibc version 2.15 to work, but the dCore wheezy image only has 2.13, as usual...)
And if force-loading a package is a no-go, how to manually update libc6?