The answer may be coming too late for the person that asked this question. But I am recording the solution here for the benefit of anyone else that may need this information.
I just tried this out with our newly upgraded (2.8.2) cruisecontrol and it really works fine.
Use the labelincrementer task to get some flexibility in this fashion:
On your config.xml use the task:
< project >
< labelincrementer defaultLabel="my.cruise.build.1" />
</project>
Make sure you dont have any serialized build files in your cruise home directory (the file will have a name <*your_project*>.ser. If you do see this file from your previous build attempts, delete it. Dont worry it will get recreated. This is required to prevent the build tasks form peekinginto this file and upping the number in the previous format rather than the new one you just specified in the config.xml
Remove/cleanup all log files from the log directory (from <cchome>/logs/<*project_name*> area) This is required to avoid the build tasks from referring into the label values form the previous builds.
Once you have done all of this as specified, run the build and you will see the label for the next build the way you specified in "my.cruise.build.1"
Look up this page if you need more info: http://cruisecontrol.sourceforge.net/main/configxml.html#labelincrementer