Thats strange but most perfomanced variant is to use ExecuteGroovyScript (or ScriptedProcessor but it same at perfomance ScriptedProc have some additional options) or External script and ExecuteStreamCommand. But I think ExecuteGroovyScript less complex solution. More General solution write ScriptedReader and use ConverRecord according to test it is not so perfomant but more general solution writing ScriptedReader you can than use it in any proc on your choice.