so many ways

ive taken so many rounded bolts off and i must say that all the above ways work.
dont knock the chisel idea, coz if he aint got a welder or the easy outs then its a way that will get him out of trouble quickly and its free.

if u can get a slightly smaller socket on then best to use a t bar and tap it while u try to turn it. this will help keep the socket on the nut and also help break the seal.