It works for me with the following hack (which I believe I found
somewhere on this group):
Place the following in config/deploy.rb:
set :stages, %w(staging production) # define your stages here
set :default_stage, "staging"
require 'capistrano/ext/multistage'
set :ec2onrails_config, {}
Then, place the contents of ec2onrails' examples/deploy.rb (tailored
to your app of course) into config/deploy/{stage}.rb.