Keeping crushed ice from melting, without it joining back together
As far as I know: No, there isn't. Because is some cases that is the purpose of crushed ice: Melting faster than an ice cube.

I don't know how many guest you have, but I would just keep ice cubes in the freezer. When making a drink, just take some out, hold it in your hand and hit it hard with the back of your bar spoon. Voila, crushed ice.

Please note that this only works with heavy bar spoons, so not every spoon available is made for this purpose.

On another note: You can also buy crushed ice. It comes in large bags. Of course the pieces also join a bit together, but here is a trick. Just throw the closed bag on the floor so the pieces separate. Then take a champagne cooler or something and put your ice in there. Put it in the freezer. It will join a bit of course, but somehow you can still take some out with an ice shovel. This how some bartenders I know do it all summer long during outdoor-events.