A Bag of Tricks that makes Lego would be cool, but easily abused.
Simply take apart the summoned creature, put the bricks into another minion and repeat.

And there wouldn't be a variation between them as the Minifigs are the only minions right now.

I'm actually thinking of creating a PrC to this (and maybe an Epic PrC or Epic Destiny).
Based around certain sets, creating a Jedi model, or a Castle Builder (well, making buildings and rooms that can be stacked up together)