在web.config中读取环境变量

Is there a way write code in web.config file using preprocessed function. Say I created environment variables like %Temp%, %WINDIR%. order to read these I can use the configurationManager class. But I dont want to use it. I woudl like to use a preprocessed function similar to timeStampPattern="{timestamp(local)}". Here timestamp(local) retrieves the value directly. So in a similar way can i read the environment variables %temp% and %windir% using preprocessed function if any exists?Is there a way write code in web.config file us