How to access parent scope from within a custom directive *with own scope* in AngularJS?

I’m looking for any manner of accessing the “parent” scope within a directive. Any combination of scope, transclude, require, passing in variables (or the scope itself) from above, etc. I’m totally willing to bend over backwards, but I want to avoid something totally hacky or unmaintainable. For example, I know I could do it right now by taking the $scope from the preLink parameters and iterating over it’s $sibling scopes to find the conceptual “parent”.

What I really want is to be able to $watch an expression in the parent scope. If I can do that, then I can accomplish what I’m trying to do over here:
AngularJS – How to render a partial with variables?

An important note is that the directive must be re-usable within the same parent scope. Therefore the default behavior (scope: false) doesn’t work for me. I need an individual scope per instance of the directive, and then I need to $watch a variable that lives in the parent scope.

A code sample is worth 1000 words, so:

app.directive('watchingMyParentScope', function() {
    return {
        require: /* ? */,
        scope: /* ? */,
        transclude: /* ? */,
        controller: /* ? */,
        compile: function(el,attr,trans) {
            // Can I get the $parent from the transclusion function somehow?
            return {
                pre: function($s, $e, $a, parentControl) {
                    // Can I get the $parent from the parent controller?
                    // By setting this.$scope = $scope from within that controller?

                    // Can I get the $parent from the current $scope?

                    // Can I pass the $parent scope in as an attribute and define
                    // it as part of this directive's scope definition?

                    // What don't I understand about how directives work and
                    // how their scope is related to their parent?
                },
                post: function($s, $e, $a, parentControl) {
                    // Has my situation improved by the time the postLink is called?
                }
            }
        }
    };
});