[ccnet-user] How to use CC.NET label in a exec task?

[Chagel]

I want to zip a file with the name of time stamp.
Tried to use CCNetBuildDate label like below, but failed. Any idea?
I dont want to use NAnt if that's not the only solution.

<exec>
  <executable>C:\Program Files\7-Zip\7za.exe</executable>
  <baseDirectory>E:\BuildRoot\Eagle\build\Staging</baseDirectory>
  <buildArgs>a "Executive Suite 3.5 Setup Build ${CCNetBuildDate}.zip"
"E:\BuildRoot\Eagle\build\Staging\*"</buildArgs>
  <buildTimeoutSeconds>600</buildTimeoutSeconds>
</exec>