Yes, you can. In the example above, you don't need the $ in the second and subsequent entities or associations in each XPath phrase. You'll traverse the associations starting at the object you pass in and then proceed from there. If you ht CTRL-Shift in the Modeler, Mendix will offer you a context sensitive list of objects/associations/attributes that you can use based on what you've already entered.
Hope that helps,
thank you so much, btw, my name is Stephane (man) from Montreal ;-)