How to conditionally apply a template via custom Angular directives?

You might be able to use a template function. According to the docs:

You can specify template as a string representing the template or as a function which takes two arguments tElement and tAttrs (described in the compile function api below) and returns a string value representing the template.

function resolveTemplate(tElement, tAttrs) {

}

angular.module('MyApp').directive('maybeLink', function() {
  return {
    //...
    template: resolveTemplate,
    //...
  }; 
});