What's the best way to cope with variables that depend on other variables

[tkrugg]

Say for example I have two variables

{
   "port": 3000
   "url": "http://site.com:{port}"
}

I'd like that when I call nconf.get("url"), I get "http://site.com:3000".
I tried

nconf.set("url", nconf.get("url").replace(...));

but it seems that once a variable is "loaded" into nconf, it's impossible to override it.
Question 1: can I force nconf.set to override a variable that's already been declared?
Question 2: what's the recommended way to cope with variables that depend on each other?

[tkrugg]

it looks like i just posted a dup of #197 #187 #166