Well, I got one out between showers this afternoon. Think I may have found a
fairly easy way....
Decided to try drilling it out, but the only decent quality, sharp drill bits to hand were a 3mm long series, a 17/64" and a brand new 11mm. The 3mm went in fairly easily, but knowing it would snap given half a chance, I went in about 6mm, opened it out with the 17/64, then a bit deeper with the 3mm. After about 15mm, thought I'd try the 11mm - as stealthe suggests the end just shears off. (the end bit's about 18mm diameter, but necks down to about 8mm diameter about 5mm in - designed this way to snap off if you try to turn it)
As you can see from the pics, I virtually drilled the head off down to the M12 threaded section, but you don't need to go this far. I unscrewed it after hammering my 1/2 - 3/8 impact socket adapter into the 11mm hole, to a depth of about 6mm
I reckon you only need drill it about 8 mm deep, which is fairly easy with good quality HSS bits - the 3mm was about blunt after one bolt and I'm hopeless at sharpening them, so I'm gonna get a few more small bits before I do the others.
The security key pictured is the wrong one for this bolt
Sorry about the picture quality. I'm hopeless wiv a camra too
