You can do it. Notice that all DNS CNAME entry point to the same host.
1:
github.com/florianwolters/florianwolters.github.com
CNAME file content: blog.florianwolters.de
DNS CNAME: blog > florianwolters.github.com
2:
github.com/florianwolters/pear/tree/gh-pages
CNAME file content: pear.florianwolters.de
DNS CNAME: pear > florianwolters.github.com