Add additional model to model hook triggered from link-to

I'm happy that multiple models can be loaded into a route using something like this (although feel free to correct if there's a better way!):

 model: function() {
        var self = this;
        return Ember.RSVP.hash({
            foos: self.store.find('foos'),
            bars: self.store.find('bars'),
        });

However, if the model hook is set by a model being passed by, for example, a link-to helper, how should I add the additional model?

Thanks!