Blanket Purchase Orders - best practice?

As an manufacturing company, we have many blanket POs that we send to our vendors. The releases are NOT necessairly at set intervals or for a set number. Has anyone found an easy way to mange blanet POs?

Here is what we are currently doing, but it's too many steps.

I've created a customer record called "Work Order" aka WO. This was before NS came out with their Work Order (so please do not mix it up with their terminology). I have WO as a child record to the PO. When we want to initiate a release, I complete the WO form. I have also created an email template for the WO. So from the WO, it populates the email, which is sent to the manufacturing plant.