How can I record partial payments on draft orders in Shopify?

[mbeffa]

We receive Purchase Orders which we have to enter as draft orders. Most of the times we have to make partial shipments, which can be captured in the Orders interface. After or before a partial shipment, the customer makes a partial payment through bank transfer, check or money order. Incredibly there is no way to capture the payment on Shopify. We need to track the payments with paper and pencil. The "Collect Payment" button has only two options, "Enter credit card" or "Marked as paid". It seems an incredible shortcoming which Shopify is ignoring. 

To make this more clear:

When I select "Fulfill items", I can select one item from the order and I can make a partial fulfillment: 

When I select "Collect Payment", I should be able to do something similar. Text box to enter the amount.

Instead, I have only two options:

This seems to be an incredible short sight. Any ideas?