Configure Rails application per run and not per enviroment

I've got a Rails 3 application with some functionality I've written that
I only wish to be active if I've specified it to be active for that
application start alone.

I can't see how I would do this with initializers or the standard
configuration strucuture as they are set per environment and and I don't
want to have to go and change a configuration file everytime I want to
switch my functionality on or off.

Ideally a command-line switch would work great...

    rails server -run_my_functionality=true

... but I can't see anyway of making this work in Rails as it simply
throws out my custom argument as unknown.

I'm using JRuby to run my application, but I don't believe there is
anything extra that is gives me to help with this.

Any way around this or anyone come up with a neater solution for per
start configuration?

Cheers

Set as an environment variable, e.g.
prompt% run_my_functionality=true rails s

Then it's available in an initializer, environment.rb or wherever as

ENV['run_my_functionality']

HTH!