This "does a piggyback FAA PPL need a BFR" business has been done to death on every pilot forum going, and people have got written replies from different bits of the FAA which directly contradict each other.
It will remain a grey area until somebody obtains a ruling from a higher level of the FAA.
It is just like the other old chestnut: "does a JAA PPL meet 61.3" e.g. can you fly an N-reg in Germany on a UK issued PPL?
And there are some more. Night flight in the UK (in any reg plane), not under SVFR, on an FAA PPL with no IR.
We could collect these up
