creating a new currency for airline miles

[cognitive.libertarian+ml at gmail.com]

I'm wondering how GC users account for airline miles.  

Since Continental Airlines is in the Star Alliance, presumably the way
to set this up is to create an asset accout "Assets::Star Alliance".
And since Star Alliance miles cannot be mixed with any other kind of
milage credit, it must be represented as its own currency.  

It doesn't appear possible to create a new currency.  So I can only
think of a couple hacks:

* hijack and repurpose an existing obscure currency that you're
  unlikely to ever use

* create a stock account, and treat each milage program as stocks

What do people generally do?