User defined tag in spec file

rpm -q --qf %{CONFIG_FILE_LOCATION} <RPM_PACKAGE_NAME>

where CONFIG_FILE_LOCATION is not the predefined tag .

What should I write in the spec file to enable this kind of option ?

or is there any anyother way by which user queries the rpm to know the
value of user defined VARIABLE( like CONFIG_FILE_LOCATION).

Any help or pointers will be appreciated.

Thanks ,
Pramod