I don't suggest that primary teaching is simple - but it doesn't require deep subject knowledge, therefore presumably you don't need trainee teachers to have that knowledge, just a high quality individual who can learn how to do that sort of teaching and pastoral care?
Surely the universities who are teaching ATPL subjects in house are using PGCE or PGCert in same way they do for other subject matter instructors? (I did the PGCert when I was a university lecturer - which is more tailored to adult learners).
G