You can still enter all of the purchases via the receipt hub, you just don’t mark them as paid if you haven’t paid them.
When you say most of the purchases are via invoice though, what do you mean? The reciept is exactly for this purpose, you upload all of your receipts and invoices and create purchase invoices for them from there. Then when you pay the purchase invoice you mark it as paid up, either by bank tagging or manually assigning a payment to the purchase itself.