Figured this was worth sharing - credit to IAang gaming (no idea who that is, just found it randomly :)):

http://iaang.com/cb

I plugged in some basic stats to see how it works - seems pretty nifty. I did Easy Double Maneater, with Fayne, Brakus, and Martyr. 5000 ATK, 100 CR, 220 CD on all of them, except Martyr, who I set up with 5000 DEF. Calc doesn't let me put Fury set in, so I used Savage/Cruel on all of them. Gave me roughly 1-Key UNM. Curious if it'll pan out like that :)

If anyone else is bored and wants to dump their comp in, let me know how close it is to your actual! Sadly it doesn't work for my normal comp - debuff extend isn't supported :(

A few notes from my experimenting - you need to check the "Show Multipliers" to see the damage. Also, make sure to click the "Stats" button and enter the stats for your champs.