The only thing I can recommend is this: minimize your aggravation.
Put that bottle in the background on the left side of the screen, where there are no tiny droplets. on a separate layer, roto around the splash that comes out of the glass, and THEN use the blending modes on it.
This shot won't be any piece of cake.
The first place to look is the color channels. Look at Blue. It's almost a perfect matte just the way it is. Invert it and a little levels call and you should be good to go.
There are a bunch of ways to adjust the blue channel. The easiest is probably with Set Channels and Levels. The simple approach is to use Set Channels to set the alpha to the blue channel then use a levels call to the alpha channel and adjust the black , white and gamma points to make the alphe look the way you want it to look.
Another way would be to use the levels call first on the blut channel, then apply Set Channels. The quality of the preview is so poor that I don't know which way would work better.