application.html.haml

!!!
%html
  %head
    = csrf_meta_tags
    = stylesheet_link_tag "application"
  %body
    = yield
    = javascript_include_tag "application"
    = render_inline_javascript_controller_action_asset

inline_js_asset_helper.rb

module InlineJsAssetHelper
  module SprocketsActionViewContextHelper
    def self.context= context
      Thread.current[:SprocketsActionViewContextHelperContext] = context
    end

    def self.context
      Thread.current[:SprocketsActionViewContextHelperContext]
    end

    def method_missing method, *args
      SprocketsActionViewContextHelper.context.send(method, *args)
    end
  end

  def render_inline_javascript_controller_action_asset
    render_inline_javascript_asset params[:action]
  end

  def render_inline_javascript_asset(name)
    app = Rails.application
    assets = app.assets
    helper = Sprockets::Environment.new(app.root.to_s) do |env|
      env.js_compressor = assets.js_compressor
      env.append_path("app/views/#{params[:controller]}")
    end

    # Stash a reference to the rendering context on a helper module we can mix into Sprockets renderer
    SprocketsActionViewContextHelper.context = main_app.routes.url_helpers
    context_assigns = assigns
    helper.context_class.instance_eval do
      include SprocketsActionViewContextHelper
    end

    # Copy the instance variables from this ActionView rendering context onto the new Sprockets rendering context
    # by hooking into the initialization
    helper.context_class.instance_eval do
      define_method :initialize do |*args|
        context_assigns.each do |k, v|
          instance_variable_set "@#{k}", v
        end
        super *args
      end
    end

    asset = helper.find_asset("_#{name}.js")
    javascript_tag asset.body if asset
  end
end