[Zope] Reverting to previous version of Zope

I have a system running Zope 2.7.2 but because of a critical bug (http://zope.org/Collectors/Zope/1401), I'd like to revert to Zope 2.7.0. I have Zope 2.7.0 installed, but in my instance directory I changed zopectl, runzope and zope.conf to point to Zope 2.7.0 but it still invokes Zope 2.7.2 (at least according to what Control Panel says). How do you control what version of Zope is run? It seems like there are all these environment variables (in the files I listed above) but none of them seem to actually affect it?!? Any suggestions? -- Mike