The only idea I can think of is:
- You have access to certain CC.NET variables.
http://build.sharpdevelop.net/ccnet/doc/CCNET/Integration%20Properties.html
If you write your build logic in msbuild, you can check these values (listed in the url above). I'm not sure if there are any in there that meet your requirement.
I think of CC.NET as a "big fancy msbuild.exe caller"...........
You can look at these as well.
http://build.sharpdevelop.net/ccnet/doc/CCNET/Dynamic%20Parameters.html
I don't think you can do what you want, but here are some hints.