Is it possible to summon multiple mobs at once?

After some searching, I found that MinecraftForums user Skylinerw has found a clever hack to spawn multiple mobs by using the 'riding' tag, and then separating the mobs afterwards. The original post can be seen here: http://www.minecraftforum.net/forums/minecraft-discussion/redstone-discussion-and/350423-multi-summon-summon-multiple-entities-blocks-w

The "Riding" tag can allow you to summon more than one entity. The main issue is the entities are stuck riding one another. To overcome this, an Item entity separates each entity that should not be riding the previous entity. This Item has an "Age" tag of 6000, which despawns the item the moment it is summoned. All entities riding the items will automatically appear at the bottom of the stack without taking any fall damage.

The limitation is the area the entities are summoned.