Conditional before() blocks in spec_helper based on metadata?

I have some tests that need to load my application’s seed data prior
to running, and others that don’t. It’s a well-defined set of

describe "needs seed data", :needs_data => true do

What can I put in my Rspec.configure { … } block so that every test
which has “:needs_data => true” will invoke a particular before(:each)
{ … } block? Note that I still want every test to run; I just want
the :needs_data tests to get some special setup first.

~ jf

Look at this example for javascript pages:
javascript.rb · GitHub.
I think you can do something like that.