I waited awhile for some replies before answering.
There is no benefit to doing any kind of external fuel additions on a computer controlled engine.
The system is an original design with program that has been worked out by engineering and test.
The system runs on feedback from sensors to keep the operating conditions within tables of values, in program.
Any effects of external additions to the airflow is sensed by the OX sensors such that corrections are made to fuel injection to "counter' the effects of this additions in the mixture.
The same can be said for an additive to absorb water in the gas.
It is alcohol based same as Methanol such that while absorbing water it leans the mixture.
The Ox sensors detect the extra oxygen produced from the Methanol just after combustion and in return, the signal adds more fuel by injection, causing a loss to normal fuel mileage.
If this were to go to extremes, a code 171/174 could result. The same condition has been reported with the use of 'high concentrations' of Ethanol in gas formulations used in non flex engine control systems.
It moves the 'fuel tables' out of limit causing the codes to set as a normal system response.
Additionally, adding an alcohol into the air stream between the air filter and mass air lowers the temperature of the air stream. This might be perceived as an increase in torque from the motor but you pay for it in terms of using extra fuel for a number of reasons. Those reasons are the intake air sensor detects the lowered temperature and causes added fuel much the same as the OX sensor will do detecting the extra oxygen, so you can get a double hit for it in terms of extra fuel consunption.
As another effect, the mass air meter is cooled and results in a change of transfer function signal. The reason is the air meter is a hot wire bridge and is cooled to excess by the presence of the alcohol in the air stream.
You can see from above:
If the control system were altered, sensor hardware design changed and engine compression raised, it could then be of benefit.
The flex fuel engine systems are altered for this extended fuel use by system programming change and hardware changes that are able to detect these changes in fuel as they are passing through the system..
These examples are the basis for not realizing any benefits to the efforts in a stock non flex fuel control system.
The question of additives and devices was just asked in my local newspaper but the correct and best answers are never given the public such that the question just keeps being in float since the explanations why are never offered. I assume this is why the question appears in these forums, as well.