Magic classes for Overloaded Record Fields, overlaps, FunDeps

[AntC]

There's an intriguing comment here wrt anonymous records:
https://ghc.haskell.org/trac/ghc/wiki/Records/OverloadedRecordFields/
MagicClasses#Designextension:anonymousrecords
(End of the section)

"... this doesn't quite work, because the two instances overlap,
 but it is possible with a bit more trickery"

I could well understand if everybody's forgotten what was the "trickery", 
because ORF has been so long in the pipeline, but could anyone explain?

Reason for the q: I'm looking at anonymous records myself,
 including extending, shortening and joining anon records. 
And yes overlapping instances are everywhere.

Using type families isn't being too ergonomic. And I notice ORF has used FunDeps.
But for me, FunDeps in the HList style is also rather ugly.

Is there some trickery I'm missing?


Thanks
AntC