Rails - Jan 2006 - relationships in text fixtures

I''d like to be able to do something like:

--- x.yml ---
x1:
   id: 1
   ...

--- y.yml ---
y1:
   id: 1
   x_id: <%= xs(:x1) %>   # Instead of hard coding ''1''


   but I haven''t found a way to make it work yet.  Is this even  
supported?  Any hints?  :)

-tim