For more simple systems, like FiTech, folks just increase the engine displacement figure to get the VE table in the ballpark. the ECU doesn't need to be told it's running E85, it doesn't really care. Just help it by saying the CID is larger than it is.

I run 50% E70 ["E85"] and 50% 93 octane to run ~E40 in my 'Cuda, it's good for about 100 octane, mixing is easy and my timing is conservative enough to manage ethanol variance.