That's a great idea MartinP! I've been putting off looking into to get one made up, because I have a sneaky suspicion it will be very expensive. If a flat one would work, that will make it a lot easier/cheaper to source one.
Raphael - I would be very interested to know whether you are in fact using a Durst board, because that may well be easier to find. I have had no luck with finding a meopta one. I'm told they existed (once) but haven't had any luck finding one yet.
Thanks for the tip on the retaining ring also. I didn't know these existed, but don't seem difficult to find, or particularly expensive.
Thanks guys - I have hope again!