If I understand the OP correctly...
He is doing the
FAA to JAA IR conversion, and he has to log at least 15hrs dual, at an FTO.
In reality, he will not pass the CAA IRT after 15hrs, regardless of his aviation experience, unless he has had some pretty on-target training beforehand. This is simply due to the NDB etc hand flying, which "modern pilots" don't do. And a non-owner is likely to be even less current...
Since this training won't count for anything, it doesn't need to be logged.
There is no new theory or procedures to learn. The JAA IR is just old-style "classical IFR", with a load of little bits added like calling out "ice check" every 1000ft in climb / every 5 mins in cruise, until the FE says you can stop.
So he just needs to find somebody who knows the protocol and is able to pass it on.
Then he needs to rent a plane which resembles the one the FTO will operate - otherwise a load of currency on type will be wasted.
Why not find a suitable FTO and rent (self fly hire) one of their planes, and fly with this "chap" as a passenger?