As actually I end up installing Tg2 on various systems having python2.6 quite often I have patched the bootstrap script to work on it.
If you had problems installing TG2 on python2.6 failing on Extremes or Zope dependencies you can try to use this script, it should work for you:
https://bitbucket.org/_amol_/tg-bootstrap-py2.6/src/tip/tg2-bootstrap.py