On Sat, 28 Nov 2009 22:58:00 +0000 (GMT), Dave Plowman (News) wrote:

I could cut a cross with a Dremel to provide the centre?

If you can do that why not just cut a slot and use a parallel sided
(not wedge shaped) straight screwdriver after the soak with
PlusGas/Diesel? Gentle use of a powered impact driver might be better
than a hand held tool. How much pressure can you apply to stop any
driver turning out without distorting the bit you want to keep?

--
Cheers
Dave.