custom variable in config files

hi - is it possible for me to declare a variable in one inlcuded config file, which is then visible in all the config files? in order to keep the config file as simple as possible, i want to take out the site/server dependent portion into a variable. so at each different site/server i would have an included file with a variable "location=london" or "location=paris" and then this is visible in all other config files eg users: test@${location} .... etc clients.conf shortname = abc.def.${location} is this possible? tariq