Create your own map, filling it with as much water as possible. In the middle, put an Ice Mage (at level 12) and near the corner, put an enemy Clutch Bearer and an ally Grunt. Save it, and load a skirmish game in single player mode. Select the map you just made and load it.
Use your Winter Storm in order to freeze the water tiles, then use your grunt to use the skill "Push" to shove the Clutch Bearer off the map (unlocks the Bouncer achievement immediately as well). Repeat this map until you've frozen enough tiles to get the achievement.