Alternatively, have you tried checking out the QuickBooks App Store for a tool that can help you manage your sub-assembles?
Katana Smart Manufacturing Software integrates with your QuickBooks Online account, so you can easily track and manage your multi-level bill of materials, while still being able to track your finances with QBs. WIth Katana you can:
Track your finished goods & material availability;
Manage your bill of materials (product recipes);
Priority-based production planning;
Multichannel sales support;
Manufacturing floor-level control; and
Manufacturing cost calculations.