I also have found that the Exped valves take a lot of getting used to! I do have the Schnozzle, which helps a little. Mine is the UL7 Downmat, which is not as comfy as I'd like but does work for me.

I have used a heavy trash bag as an inflator, too, on other pads with standard valves. It is possible to close off that cut corner to make it waterproof! Use the same twisting and then bending over itself closure you would use at the top to make a waterproof closure.

Of course the Schnozzle can be used as a pack liner, too.