Rear wheel speed sensor removal help needed

[Sandman]

My car is due its MOT this week and for some stupid reason I left it till the last moment to get the abs/traction control/tyre pressure lights to switch off.

I though I would try replacing the wheel speed sensor first and if that didnt work I would replace the bearing.  I immediately ran into a problem when I tried to remove the bolt holding the sensor in place.  It was very tight so did everything thing right and soaked it in plus gas then hammered my allen socket home for a good tight fit and.......the bolt rounded off.  Arghhhhh!!!

Space is very tight in there (working from within the arch).  Does anybody have any tips on how to remove this now or is it now a garage job?

[chimp400]

They are a pita to do on any car, ive not done a golf but most others ive had a go at have required the bolt drilling out as it sheared off.
You could try tapping the head of the bolt around with a good sharp small chisel but i dont think it would work.