How to install core plug on Vauxhall combo N reg?

i have already asked this question & received a useful answer off someone but i forgot to explain that the core plug thats popped out is at the back off the engine & access is very hard its right by the injector pump there are pipes & allsorts in the way. is there anyway of gettin a permanent plug back in there without lifting the engine out? as i can't even swing a toffee hammer in there. thanx 4 any answers i'm desperate 2 sort it as i need it 4 work.