You can create those tasks (paint, drywall, and windows) as a sub-account for your Subcontractor Expense. This way, you can assign specific tasks to your bills, and have them all show up under the Subcontractor Expense account.
Here's how to create sub-accounts:
Highlight the Accounting tab, then select Chart of Accounts.
Click the New button.
Create a new expense account. Ensure that you tick the Is sub-account checkbox, then select Subcontractor Expense.
Tap Save and Close when done.
As for what you mentioned about the Products and Services page, I'm thinking this is related to the expense account assigned to your products. These are limited to inventory types though, so it won't be applied to services or non-inventory types.
So I can import my whole list of 150 +/- items, specify them to "subcontractor" or "material," or whatever expense account. Then, when I run my P&L statement, like you mentioned, I don't have 150 lines of sub-accounts, I just have the few expense accounts I use.