gistfile1.js

module.exports = function(Model, options) {
    var mergeQuery = require('loopback-datasource-juggler/lib/utils').mergeQuery;
    
    var _ = require('lodash');
    
    var scopes = options.scopes || _.keys(Model.scopes);
    var validScopes = {};
    
    _.each(Model.scopes, function(scope, name) {
        if (scope.modelFrom === Model && scope.modelFrom === scope.modelTo) {
            if (_.include(scopes, name)) validScopes[name] = scope;
        }
    });
    
    Model.mergeScopes = function(scopes) {
        var self = this;
        scopes = _.flatten(arguments);
        var merged = {};
        _.each(scopes, function(scope) {
            var definition = validScopes[scope];
            if (definition && _.isFunction(definition.params)) {
                mergeQuery(merged, definition.params.call(self) );
            } else if (definition && _.isObject(definition.params)) {
                mergeQuery(merged, definition.params);
            }
        });
        return merged;
    };
    
    var applyScope = Model.applyScope;
    Model.applyScope = function(query) {
        var scopes = [].concat(query.scopes || query.scope || []);
        if (!_.isEmpty(scopes)) {
            mergeQuery(query, this.mergeScopes(scopes));
        }
        applyScope.call(this, query);
    };
    
};

Nice mixin, that works good. Thanks.
Obs: in this line include() should be includes()

@marcoskubis you're welcome! _.include vs. _.includes depends on the lodash version used.