Need ideas for removing blueberry stains from concrete

Last July we got 10lbs of blueberries from a farm in Michigan. The boys had just seen the film 'Despicable Me', and they thought it would be fun to have some minions of their own. So they took the blueberries and started doing some experiments with them.

The blueberries weren't organic (and were possibly genetically modified as well), and the experiment went badly. The result was 10 lbs of very mad, very vicious, cannibalistic blue fruit!!! (They ate our camera, so Kire drew a picture of them.) 

We didn't know how to kill them, so we locked them in the basement until they ate each other. 

Unfortunately, now we have some very messy blueberry stains all over the basement concrete. So, if you have any ideas for removing the stains, send them our way!