I bit the bullet and introduced my two pairs of mice this afternoon (after weeks of having nightmares about it! :-O ) - and it went beautifully! :\">
I used a dab of watered down vanilla extract on their bums and it seems to have done the trick nicely. Lots of sniffing, a little grooming and squeaking, but absolutely no fighting like I had with Dolly and Grace meeting. They're settling into a mini duna for now, with piles of bedding but no toys.
I've decided to switch to feeding them broken up Selective Science biscuits until they're settled with each other, in the hopes that this will discourage fighting over who's got the best treat! They've got a millet spray too, but currently they're curled up in a couple of little furry piles. :\">