List/Fetch/Calculate project spend via API

Hi, I am building some reporting extension and I am trying to show spend per project. I can use Project_TagSearch to get the list of projects and store the TagName(s).

I can then call Invoice_Search and provide TagName to get the related invoices (INCOME) for a project, but there is no way to do this for Purchase_Search (EXPENSE).

There’s a feature request below but I’m wondering if there is another way of obtaining the purchases related to a project via API?

Thanks