We use QB Enterprise, so I'm not sure if this process works for Online, but we have an ugly workaround for this problem.

We created an "Other Current Asset" account called Items Pending Receipt. We can then enter the bill with quantity = 0 for all the Items, but put the full pre-tax value of the items in the Expense account. When we later receive the items, we delete the Expense entry and add the quantities received to the Items tab.

This does create yet one more thing to audit, but it solves the problem of entering bills before the inventory arrives.

Overall, it amazes me that this feature does not exist natively in QuickBooks. Our distributors send us the bill the same day that the item leaves the warehouse, and it can take days to weeks for it to land. That can create a messy backlog of payables if we don't get the bills in promptly.