I'm sorry to be vague but I seem to remember there being some kind of requirement that a Transport Cat aircraft had to be 'singly' owned to be used for training. I don't want to pee on your fire here and I could be completely wrong - but it might be worth checking the ANO/AIC for clarification.
I guess I'm saying don't rely on Pprune as the regs are written down somewhere; I just can't remember where!