Pouring a new, sugar free, liquid in should cause it to dissolve as well. Be it liquor or water, heated would make it happen faster. Not sure if that’s what your after though.
Actually, I initially thought the microwaving would melt the sugar, at least a little. I just wanted to get it out, and that’s all I could think of.
The heat didn’t melt it, just helped loosen it. (The silver on the labels doesn’t spark, either.) Not sure if it loosens because of the heating of the sugar or the heating of the bottle.