Answer
Build a custom PL/SQL package function that accepts the incoming file content as a CLOB parameter, parses/extracts the needed values from it (for example using a cursor over the parsed structure), and inserts them directly into the custom LU's underlying table. Configure a Routing Rule and Routing Address so that when the File Reader picks up a new file, it calls this custom function directly with the file's content — this gives the custom LU an equivalent ingestion path to what a BizAPI would normally provide, built entirely in PL/SQL since no BizAPI exists for that LU.