Use a Dremel with a fiber cut off wheel. Go a little deeper than a score would then try snapping, if this dont work use the Dremel and grind all the way through. If the glass is lime, pyrex or quartz glass heat can be used, You dont have to get it molten just red hot, use MAPP gas, then use shears or tin snipps, if its at the right temp it cuts like paper, but tends to stick to the cutting edge. If its that cheap ordinary, sheet or window glass just use a file and sand paper. Concrete works well as a sanding device. Hell I've heated up and ground down piles of glass, just for the fun of it. I hate the type that explodes as its cooling down, cool down that type in an oven slowly.