Answer
Yes — pass the PL/SQL block itself as a parameter to Fnd_Event_Action_API.Action_Executeonlinesql, and post that call as a deferred background job using Transaction_SYS.Deferred_Call; this lets you defer an arbitrary block of PL/SQL logic to run as a background job directly from an event, without needing to first create a standalone custom procedure solely to wrap that logic for deferral.