A couple solutions you may want to consider:

1) Buy some cheap nail polish in a translucent
champagne color and paint the inside of the glasses
with it. Use a larger brush than the applicator inside
the bottle-cap and be sure to get the rim perfectly
level.

The problem is, when the glass is dropped, the
"liquid" doesn't move and the action afterwards has
to be faked. Plus, the champagne glasses are
non-returnable after being painted.

OR....

2) VERY tiny glass or plastic beads (available from a
craft or hobby store) in champagne color. The
advantage is, under the lights the beads resemble
bubbly and can be "poured" from the bottle into the
glasses and -- after they are spilled -- can be
vacuumed or swept up and used again. On carpet
the spillage will be silent.

Cheers!