Peter,
In the absence of any suggestions from closer to home it might be worth your while contacting Alex Mitchell at Spencer Lane-Jones,
alex@spencer-lj.com , who do a big brake vented conversion. I don't know whether this involves the modification of any existing bits.
My 410 is pending this conversion. It will out stop many a modern car but the heat can build up to the point that the fluid boils...... somewhat disconcertingly!
Roger Morrall