[gwnn]

I remember reading about this convention on BBF, does anyone have a good structure?

4c=p/c
4d=good raise in hearts
4h=nat
4s=nat
4n=ask for minor

springs to mind, but maybe there's a more clever way?

Also, what range would you use? Presumably it's not a bad idea to include a few minimum openings too.

[hrothgar]

Seems like a VERY rare bid. With this said and done, let's start with the two "known" bids

4♥ almost certainly should be to play
4♣ needs to be pass or correct

Next lets look at 4♦.
My immediate reaction is to use this as an asking bid focusing on the minors.

You could use

5♦ = Diamonds and a minimum
5♣ = Clubs and a minimum
4N = Diamonds and a max
4♠ = Clubs and a max
4♥ = max with concentrated values in Hearts