How about using a cheap ethanol / gasoline separator. (I have never seen one.) That would bring the RVP back to what we had before this EPA madness. With the separator you could dump the excess ethanol in the exhaust just like the thermosan units, or you could mix it with water and put it in the black tank for later disposal.

We have guys at the airport doing this separation with water but it is a standalone operation. We have never found a use for the removed ethanol and water mixture, so it just gets dumped. I'm sure the EPA is not happy about that but they are the ones who caused the problem in the first place.