A late entry to the discussion...

Two other options (maybe) for non-stock

Option 1
Can we have an item with a standard cost of $1 in the assembly and have that cost add to the assembled cost? The actual cost would be $0, so the entry would be to inventory and the variance account...
If you want to add $10 assembly cost to the item, you would add 10 of these items to the assembly

Option 2
create a labour inventory item - avg cost
create a new account set - labour
point the inventory control account to the 'applied labour' account in your gl
Do an adjustment to inventory to add 1,000,000 labour hours - dr and cr to the 'applied labour' account.(net $0 to GL)
every time an assembly is done, the applied labour account is credited and the inventory account is debited.