You may be able to fake a liquid by doing a texture so part of the glass is a different color , and using a transparency map on a disc or plane to make the top surface.  I use a modelling program to make a plug, that fits into the glass to be the liquid. There are also some props with morphs for level and tilt of a liquid in the glass, bottle etc .

"Champagne Flute Glass Prop" in freestuff might work.