Is there such a thing as waterproof gloves?
My latest trick is to wear Spesh BG long finger gloves (very light and thin, and have gel padding). If it's wet then they get soaked through but, since there's not much material to them (and therefore they don't hold much water) they tend to stay quite warm.
If my hands do start to get cold I'll put on a pair of Altura Altitude waterproof gloves over the top of these. These are fleece lined and putting them on over wet long finger mitts just works for me, my hands warm up in no time even though they're still wet. The whole lot does get soaked, but the important bit is that I stay warm.
Warm and wet is easy to cope with.
I packed on the BR600 at Galashiels last year because of the weather. I was just miserable, slow and it wasn't going to get any better.