I was just thinking, about having each narc at their own table at a wedding reception, and have thought up another 'not so small' refinement.
It would be really evil - and only to be done it you were breaking all contact after a wedding, but -
how about letting the narc 'dm' have her way - book everything where she wants, venue, menu etc, invite all her friends - and then just piss off with your intended and a couple (or more) of your own friends and have your wedding where you want, and how you want?
When dh and I got married, we did discuss (briefly) getting married in the church I'd gone to some 50 miles away from home. I was on the electoral roll there so it would have been possible.
Cue dm "If you get married in Manchester your father won't be going and I won't be going either".
She was really mean, too. For example, if a recipe serving 4 needed a tin of tomatoes and she was doing half, she'd put half a tin of tomatoes in the fridge where it would go mouldy. Once at our house for the weekend, we had bolognese and my poor df remarked 'that was really tasty'. Cue dm in a squawk worthy of the café owner in Monty Python's Spam Song "It was only mince".
Another time - might have been the same weekend - feeling like throwing up during a very heavy period - I was peeling grapes do make Sole Veronique for dinner. Inbetween the grape peeling I was waiting on her hand and foot - and dinner was a little late. Said with a sniff "A ham sandwich would have done".
Think that was the same weekend she walked into the house, plonked her arse down on the settee and said "I'm not going to do a thing all weekend" - she was true to her word, too 
I did think of getting my dm to sign the form - in the guise of witnessing my signature - to leave her body to medical science. Then after she died, there would have been no funeral, and all the people who didn't know her would have been saying what a wonderful thing she'd done, leaving her body to science. She'd have probably ended up on a slab being dissected by a hung over medical student. Otoh, they might have found something really strange from a physiological pov, which could have been quite interesting - missing heart for example. A counsellor I was seeing at the time thought it was brilliant and said that revenge fantasies are very good therapeutically.
The week before I was 19 I broke off my engagement - to a narc, natch. The Sunday was Mothering Sunday, and so I went home on the Saturday morning to give her a card/present and to tell my parents I was no longer engaged. When I told dm her only comment was "I wish I'd done the same thing".
And breathe - the cost of psychotherapy has already passed the £20k cost and is ongoing - but this is quite good fun even though it's sad for all of us that it's necessary.