Remove seized heater plug in L series head

Trying to replace all heater plugs in "99 Freelander & no.2 plug is stuck in the cyl head with the top part just turning in the socket! Its the easiest of the four to get to but is there any way of removing without having to take off cyl head for machining etc?? Would appreciate any help or even ****-taking if you've been in that same dark place!