Need Help to create new Server Variable in IIS 7.5

Hi,

We need to create a new IIS server variable, that would be passed on as a token for single signon for our reporting application.

This would be a substring of the CERT_SUBJECT variable, but will contain just the "CN" portion or the 10 digit number from the CERT_SUBJECT. Entering the entire string value throws an error in the reporting application.  

Can this be done with URL Rewrite module 2.0?

Would appreciate any guidance you can provide to accomplish this.

Thanks!

SV