I've not tried this, but here's a recipe for Elderflower Champagne I got from a friend at work:
6ltrs water
Juice and zest 4lemons
15-20 full bloom elderflower heads
Spoon o vinegar
(possibly a pinch o yeast, apparently you dont always need it as the flowers have natural yeast)
750grams sugar
Dissolve sugar into 2ltrs of the water hot, then add the remaining 4litrs..then add everything else(not yeast) and cover wi muslin/towel/whatever..
After 2 days check if it looks frothy n mingin! If its not, add the pinch o yeast, give a wee stir, leave again..
After a further 4 days strain it and bottle the lovely jubbly juice, put in a safe explosive place!
After a week you can drink it, Iâm leaving a bottle a bit longer to see how it goes, and I left my first drink about 2 weeks instead just cos..itâll keep for up to 6 months apparently.