You can not do that. What are you trying to achieve ? May be done within apache conf it self.
I want to carry forward certain environment variables which we are using all virtual hosts configured in our apache web server.
e.g., #1: Virtual hosts used in dispatcher will be same as the ServerName used in our Apache Virtualhost configuration
e.g.. #2: Using environment variables to identify custom docroot in our web cluster based on VirtualHost configuration.
Dispatcher uses "Host" header to find out which renders to connect to. You can set Host header in your apache conf and then based on that configure your dispatcher. However you can not use Apache Variables in dispatcher.conf
Here is one example of setting Host header based on flush path