Wheel bolt broken at hub

[SuperHangOn]

I noticed one of the wheel bolts has had its head snapped off at the head on my new shed purchase. About 1-2mm of the remaining stud protrudes from the hub. What would be the best way of getting it out? I have been spraying it with WD40 the last few days to soften it up in preparation for battle!

FWIW the monkey fitted a nasty tyre of the wrong size while he was at it! 2 tyres are pre-historic and I have 3 different sizes & 4 different makes!

cheers