Its tough to make a fully recommendation without knowing your exact process.

Having said that, you could create a SQL script to close the line for invoicing based on a certain condition and have the script run periodically (hourly, daily, etc.), but there isn't a mechanism in the system that would normally do this. If you are actually doing the receipt of goods then you have a separate problem of making the offsetting entry to the purchases clearing account if you don't invoice it after you receive it.