Tracking invoices against a Customer PO

Hi there

I'm a long time MYOB user. I've tried searching the forums for an answer to my question, but unfortunately to no avail. 

The company I work for operates within the Mining and Resource industry. Every client we have operates based on Purchase orders:

We submit a quote -> the client approves it and supply us a Purchase Order (PO) -> we then submit staggered invoices against the PO monthly as the work is completed over time. 

Each PO has line items broken up per deliverable per person on the Job. If billings go over a particular line item budget, the entire invoice is rejected and there's a massive headache getting variations etc.

Does MYOB Accountright have a function to help tracking something like this? Currently I'm having to manually update a spreadsheet for every invoice, which is both tedious and time intensive. 

Even if native MYOB doesn't have this type of functionality, could someone possibly direct towards an app / integrationation that could help? 

Cheers

Roy