I know you already mentioned it but I would suggest using haml-js with Jammit. Simply include haml.js in your javascripts and in your assets.yml add template_function: Haml as well as including your template files in to a package. e.g.
javascript_templates:
- app/views/**/*.jst.haml
Then in your views you can include this package (= include_javascripts :javascript_templates) and Jammit will package any .jst.haml files in to window.JST['file/path']. (If you view page source you should see a javascript file like <script src="https://stackoverflow.com/assets/javascript_templates.jst" type="text/javascript"></script>)
To use these templates simply call one of those JSTs Jammit created. i.e.
$('div').html(JST['file/path']({ foo: 'Hello', bar: 'World' }));
And Jammit will use the Haml-js template function function to render the template.
Note: Be sure to point to the github repo of Jammit in your Gemfile to get the latest version that supports newline characters necessary for haml-js to work.