Here's the recipe I used for my elderflower wine this year:
3L white grape juice
1L apple juice
2.6kg sugar
0.5kg raisins (liquidised in 1/4 pt water)
juice & grated rind 5 small lemons
6 bags rooibos
2 tsp each yeast nutrient, glycerine, yeast extract, pectolase
1 sachet champagne yeast
1.6L elderflowers
I brought a gallon of water to the boil and poured over the sugar, raisins, rooibos bags, lemons, nutrient, glycerine, extract and pectolase in the primary, stirred well so the sugar dissolved and left for an hour. I then removed the rooibos bags, and added the juice and enough water to bring it to 3gal, then left to cool. Once it had cooled to room temperature I pitched the yeast. I left for five days, then took out 2L of must, brought it to the boil, and poured over the elderflowers to sterilise them, then once they had cooled I added to the primary and left for a further 5 days. I then strained into sterilised DJs and added airlocks.
Adding the elderflowers late in the process should (in theory) mean you get more flavour out of fewer flowers. That said, with the number of elderflowers there are this year you could easily just add more at the start. It's certainly simpler that way!