mavic 451 brake lever ferrules

[foz]

I've come across a problem I'd forgotten about... I have a set of mavic 451 brake levers, but they require a special, larger than usual ferrule for the end of the outer brake cable to stop it pulling through the hole where it should sit. Does anyone have any suggestions as to what I could use instead? The hole is just large enough to allow a standard ferrule to pass through, and is rounded, not square ended, so I guess some sort of domed ferrule is needed.

Thanks!