Questions about personalization or custom.pll for Serial Entry form

I'm working on a custom.pll AND forms personalization to solve an issue I have seen at many companies, but I wanted to know if there is an easier way.

The issue is that when a serializaed item is received through the PO Receipts screen (from an RMA) we want to limit the valid list of values to only those owned by the customer in Install Base, and we do not want to allow free form entry of serial numbers.

I've written CUSTOM.PLL and a Forms Personalization to handle this.  What it does is check the install base instances table for the serial number entered/scanned, and then if it isn't on the list it pops up an error dialog, then presents an LOV of valid values to select.