Hi Dave,
Keen to keep track of what solution you come up with. I'm currently building an Arrow 1200 down in Newcastle, (only done the Carbon fore-beam and working on the Dagger-boards at the moment).
I'm considering building rectangular cases with some sort of bespoke low friction plastic inserts to transfer the loads on the board and allow me the option of stiffer moulded boards in the future if I so desire. It seems to be the way most higher performance applications are going based on my research.
I floated this idea with the designers and it was met with a bit of hesitation and a recommendation against, but a few others I've spoken to on similar designs have told me that they wish they'd gone that way for some of the exact reasons your looking for a solution now. Re moulded boards, it's definitely where I'll go in the future, but circumstance has driven me to build my own, the problem I reckon you'll have is going to be the cases being bespoke to their current dagger boards will be fitment all over again, even if made 100% to plan, hence my interest in a rectangular case with removable inserts.
Another option could be to run a few thin strips of acetal or similar down the length of the case secured some how, potentially even to the boards themselves and see if that frees them up a bit loaded.
How big of a problem do you find this in your use of the boat? Keen to understand as I'd love to avoid building myself into a problem later!
Cheers
Nick