Fixtures and helper functions

I like the new fixture features for rails 2.1. However, I would like
to define a mapper so I specify the IDs to be used, rather than a
hash. This is for several simple reasons: For one, I can type the
URLs out a lot easier if the ID is 12 vs 12351231. For two, I am
maintaining will-be live data in fixtures, and when I flip the switch
and make it actually live, I would rather not have to deal with new
IDs starting in the millions.

So, I know I can do this with ERB:

@current_id = 1
def next_id
  @current_id += 1

<%= next_id %>:
  id: <%= map_name(:quicktiger) %>
  name: Quicktiger

The thing is, I will want to use this map_name function from many
fixtures. However, I cannot seem to find the right place to put it so
I can access it from all fixure files. Is there a fixture helper
somewhere that I'm not aware of?