This is intriguing. Currently if you wanted to use something like Underscore for templating, you'd have to do something like:

$('.typeahead').typeahead({
  // ...
  template: '<%- value %>',
  engine = {
    compile: function(template) {
      var compiled = _.template(template);

      return {
        render: function(context) { return compiled(context); }
    }
  }
});

This is somewhat tedious and the solution in this pull request might make this a little easier to accomplish. I just need to think about this for a bit and make sure there's no drawbacks, but my gut reaction is that it should be fine. Assuming I don't think of any drawbacks, this will go out in v0.9.1. Thanks for the pull request!

Updated your changes to work with v0.9.0, let's move any future discussion of this topic over to #137.