I had this a month or two back and this is what I did.
Ensure you start with the lower bolt first as you risk damaging the ABS sensor.
1. If you have access to a blow torch (i used a pencil blow torch), aim the point of the blue flame into the centre of the bolt (the recessed part where the allen key fits) and keep it there for a minute or two. - This will heat the centre of the bolt up thus breaking the rusty bond between the bolt and hub.
2. Clamp some mole grips (or vice grips) as tight as you can (they really to need to be as tight as you can get them) and attempt to undo the bolt.
3. This may take a few attempts, but trust me, it works.
4. Once you have the first the bolt out, clamp the grips on to the other bolt and use the carrier to undo the bolt (i.e. move the carrier and not the grips)
You may need to replace the bolts, I replaced them with regular hex bolts as at least I can get a better bite with a socket in the future.
Hope this helps.
