I've not heard Wright's instructional, and we may well have semantic differences over what's called "scratch". But to me that's just putting some buzz or rattle in a note by leaving your airway open and letting the air take its time and rattle around a bit, as if you were coughing, rather than pushing the air cleanly out through a more constricted passage, as if whistling, to get high, clean notes. And having run RNT speck calls since their first run of polys, I can assure you they'll do it.
But I see you're in Stuttgart and reckon I'd go sit with Stephens a while for some hands on help. He seems speck crazy, too.
If you think I'm wrong, you might be right.