Set the Parent as M so that MRP does plan the lower levels. BUT make sure youuse a different buyer/planner code for the parent, say "SETS". Even though it is set to M you can still purchanse it. Once you have created the PO for the parent MRP would then remove the demand for the components as there is no longer a requirement for them.
My concern with your solution is that the Engineer in our case who creates the BOM needs to know that the items will be ordered as a set. Otherwise they don't know that they need to create an item as parent for the set. I would like no parent in the BOM, I just need the separate items in it. QAD needs to make a match between demand for certain parts and the availability of those parts in a set at our supplier.