You need to have requirement for Product Z.  You can create that with Reordering rules for product Z.  Use Min / max  qty and rounding.  Product Z must have route Manufacturing. And of course a BOM where you use product X and Y as components. 

If you set the reodering rule to automatic the scheduler action will create manufacturing orders when stoc for product Z is below min qty.  You can also set the reordering rule to manual and use the menu Operation -> Replenishment to create manufacturing orders.  Will appear as soon as qty in staock is below min qty.

Manufacturing orders must be confirmed

But: From what you write it seems like you manager want to register the components as finished products, without actually doing it. If that is tha case telle you manager: Never ever transform product in the system unless you also do it physically.  Your stock figures should always be accurate to what you actully can go and count.  This is the only way to control your business correct. (I tell this for 30 years as logistic manager.)  There are other tools to know how much you have the possibility to deliver.