I'd heard freezing them before hand works.
I made 2 lots of elderflower wine this year.
1 batch I used freshly picked flowers which I removed with a comb, a bit of a chore!
The second I froze first before removing having heard that was easier. The problem I found was when they first came out of the freezer the stalks were so brittle they were coming off with the flowers more so than when they were fresh.
Also when they thawed, which was in a matter of seconds! They became limp and soggy, which also didn't help in removing the flowers.
The fresh batch were easier tbh!
This could all of coarse be down to my lack of experience and may work better with the berries!
Sláinte