Complex Work Orders - for Goods billed by Quantity?

Need to understand the roadmap for incorporating milestone and progress payments for line type of Goods.

Business has a requirement to forecast large volumes of equipment which is being ordered with long-lead times. To adequately prepare and pay these milestones which are contracted with the vendors, we need to know when to properly forecast funds.

Currently we are treating these as informative lines on a BPA, for the purpose of tracking, and draft loading Prepayments to account for this. But this is not a sustainable business practice and will need a method of practical functionally to account for this from Oracle Purchasing.