If your subscription package with QuickBooks Online gives you class tracking as a feature, you can use that functionality in Receipt Bank to assign location, client, and project classes to expense items.
Your class tracking codes will be available to you under the "project" and "client" fields in Receipt Bank. You'll notice these two fields will be present in both your supplier entries in the 'Suppliers' tab and the individual 'Item Edit Pages' in your Inbox. Those fields will be populated with your class tracking codes from QuickBooks Online.
You might also have "user defaults" per Project.