[ccnet-user] Define environment var. as a constan

[idoy]

Hi,

I have a question about defining a constant in my ccnet.config.

I defined an environment variable constant:<env WindwosDir="$
(SystemRoot)"/>
How can I define a constant using that WindwosDir ?
I tried:
<env WindowsDir="$(SystemRoot)"/>
<cb:define SourceDir="$(WindowsDir)\System32"/>

but it throws an error.
thanks, Ido