class Rake::SprocketsTask

end
t.environment = Foo::Assets
Rake::SprocketsTask.new do |t|

You'll most likely want to reassign `environment` to your own.

`Environment` instance used for finding assets.

def environment
  if !@environment.is_a?(Sprockets::Base) && @environment.respond_to?(:call)
    @environment = @environment.call
  else
    @environment
  end
end