I don't know the RJ series, but know a 146-300 with cargo hold extended range tanks.
Not a brilliant system because of the way the fuel feed works - if the system is down to minima it can take over an hour to refuel, but we get 5hrs+ out of the bird. It is a bit of a one-off aeroplane however and I'm not sure how well the mods would map to a true passenger aeroplane.
G