A jigsaw, a steady hand, dry liners and a sh!t load of patience!
Haha another way is to befriend the plasterer, theyre always after flex for an outside light or cable to connect a cooker, once you have a favour to call in get your hammer out, ask them to patch the hole with plasterboard and get your padsaw out, job done haha!
I would never fit dry liners to lath and plaster,but maybe times have become more adventureous.