What is the best way to cut a sheet cake into several t-shirt shapes without wasting too much cake?

In addition, any ideas how to make it look like a tie dyed t-shirt? I have tried adding different icing colors and then blending with a spatula but want it to look more like a circle with puffs coming out from the middle.

I am having a hard time with this technique without an airbrush. I was thinking of buying spray bottles and filling them with different food colors and trying that out but the water from the diluted food color might run everywhere. Then again, I am trying to get the look of a tie dyed shirt.

Any ideas would be appreciated.