Before I run down the "overengineered solution" path, I wanted to throw this out to the group.
We will be receiving HL7 messages via TCP/MLLP that have a PDF document stored in a single OBX segment. As the volume is expected to be somewhat high and the documents could be megabytes in size, it would be preferable to save the PDF payload to disk and replace it with a filesystem path before IRIS does it's first Save%. The idea being that we would than implement an OnDelete that would remove the file when the HL7 message is purged.