NetSuite's Demand Planning and/or MRP will take Planned Work Orders into account and still drive you to produce the lower sub assembly even if you haven't released the top level WO. We have many layers to our work orders/BOMs as well and we have struggled with this for year. Demand Planning wasn't great but it did give us the ability to leave work orders in Planned state until all the subassemblies were In Stock.
Also we did build a custom Mass Create Work Orders screen that looked at Planned Work Orders AND released work orders to drive what subassemblies we would create. It wasn't easy but it works okay.
We are implementing MRP right now and I think that will work well for us, but it is a complex/advanced module that takes some serious data management to make it effective