Question: Are there any half-official repositories for CentOS 5 with Python 2.7?

EPEL provides only Python 2.6

Answer: 
I made an RPM for this a little while ago. You can find the source RPM here

<ftp://ftp.pycopia.org/pub/python/RHEL51/python2.7-2.7.1-1TH.src.rpm>

Just do the usual `rpmbuild --rebuild ...` to create the binary rpms. It does not interfere with the installed 2.4 version, it coexists with it. but you do have to put the specific version in your scripts: `#!/usr/bin/python2.7`. But if you use setuptools invoked with that version then it happens automatically.
You can try to get 2.6 srpm from epel you've found, extract spec file from it, change version number and rebuild it.

However, be carefull: there are a lot of packages depending on python 2.4 on el5 (like yum). You'll probably need to ensure that you are installing 2.4 and 2.7 at the same time or that you've rebuild everything depending on 2.4.